(FORTUNE Magazine) – RONALD SHEADE HAS, quite deliberately, turned his life upside down. Once a vice president and assistant general counsel at a Fortune 1,000 company, he's now teaching eighth-grade science in a suburb of Chicago. He doesn't make big bucks anymore, doesn't travel to Europe on business, doesn't negotiate wickedly complicated deals worth tens of millions of dollars, doesn't even live in the custom-designed dream house that he and his wife built just four years ago. Sheade, 45, earns $45,000, a gaping 70% less as a pedagogue than he did as a corporate honcho. But he gets a real kick out of teaching, spends much more time with his two young daughters, and still lives in a comfortable, if not exactly fabulous, residence. A tall, athletic man with a level gaze and a mean jump shot, he says: "I'm probably happier and more relaxed now than I've been in years."

As Sheade's experience suggests, a whole new dynamic is taking shape in the American job market. Powered by a heady mix of fear and anger, burnout and boredom, hankering and hope, legions of ostensibly sane professionals, most on full throttle in middle life, are changing not just their jobs but their vocations. If you haven't shifted to a new career yet, chances are you've thought about it. And if you've thought about it, you've probably wondered how to do it, because it isn't easy.

Occasioning all this occupational tumult is the clash of two outsize trends. First is the relentless restructuring of corporate America, which continues to downsize, rightsize, reengineer, reorg, RIF, outsource, and outplace tens of thousands of employees every month. Second is the inexorable aging of the baby boom. As these demographic road hogs enter their late middle years, usually with spouses and children in tow, many, like Sheade, are looking for careers more in sync with their changing personal priorities. It's the Nineties version of that mythic American phenomenon, the midlife crisis.

It all adds up to a swell of graying boomers who are overworked, overwrought, and fantastically insecure about their jobs. Of the more than 100,000 managers polled by International Survey Research (ISR) in 1995, 37% said they were "frequently concerned" about being laid off--the highest anxiety level in decades. Four in ten managers said they couldn't count on keeping their jobs even if they performed well. Nearly half were seriously worried about the future of their companies.

Many of these scarified souls are seeking solace in new professions. Says John Stanek, president of Chicago-based ISR: "These people are leading lives of quiet desperation, and finally something pops. They say, 'I've got to get out of this situation.' " Indeed, one-third of employed, college-educated adults recently surveyed by the Gallup Organization said they would, if given the chance to start over again, opt for a different line of work. Some 10% of the American work force actually switch occupations every year, says the Bureau of Labor Statistics.

Corporate America, once so munificent to its employees, still provides many boomers with one last perk--a bagful of benefits that can ease the transition to a new career. In fact, a significant subset of career switchers admits to harboring a naughty little secret: a burning desire to get fired. "I kind of wanted to get laid off," confides Lisa Sheehan, 34, a former pharmaceutical sales representative in Vernon, Connecticut. Jettisoned by Glaxo in July, Sheehan sallied forth with five months of severance pay. She is now mulling a new career--in career counseling.

The business of advising people about their careers has itself become a hot career. The Bureau of Labor Statistics predicts that counseling will be the 59th fastest-growing occupation, out of the 513 it tracks, during the next decade. More than 3,100 nonfiction books about finding, managing, and changing careers have been published just since 1990. What Color Is Your Parachute?, the classic guide for career changers updated annually by author Richard Nelson Bolles, is still selling briskly, 25 years after it first appeared in print. (For some tips on counselors and books, see box.)

It seems pretty clear by now that most baby-boomers get this concept of career self-reliance. They understand that the social contract has been sundered, that corporate fealty has become a fool's errand, that the days of linear advancement--the 30-year progression from subaltern bean counter to department supervisor to division head, for example--are pretty much over. They know their bosses won't commit to anything--not to job security or a guaranteed annual raise or a company-funded pension.

They know all that. What they don't know is what to do instead. Says Marilyn Moats Kennedy, a veteran career consultant in Wilmette, Illinois: "Among baby-boomers there's this tremendous sense of stagnation. They have become miserably disillusioned. They think they played the game by the rules, but the rules have changed."

So anxious are boomers about their careers that some experts descry a whole new genre of midlife crisis. The fabled middle-aged spree--that sudden craving for a shiny sports car or a younger lover or a surgically enhanced body--actually requires a degree of stability, wealth, or boredom that most people just can't muster these days. Says Ronald Kessler, a professor of sociology at the University of Michigan and a coordinator of a large survey of Americans in their middle years: "We're not seeing people who've made it in life confronted by bouts of existential angst, asking themselves, 'Is this all there is?' What we're seeing instead is this tremendous uncertainty about careers."

Given all the handwringing about careers, it's astonishing how little we actually know about the subject. As a nation we probably have a better grasp of how and why people switch brands of underarm deodorant than we do of how and why they trade careers.

Part of the problem has to do with the way most of us pick professions in the first place; usually before we are old enough to vote, generally with only a dim understanding of what we want in a vocation, and often heavily influenced by others--our parents, our siblings, or the guy down the street who drives a Lexus.

Paul Tieger, co-author of Do What You Are, a book that helps people find occupations that match their personality types, migrated to Hartford as a young man intent on entering the insurance business, largely because his father knew someone who was successful in that industry. But Tieger later discovered he was more interested in analyzing psyches than in reading actuarial tables. Says he: "We make decisions about careers at a time in life when we're least prepared to do it, when most of us don't have a clue what we want. It's not until we reach our 30s or 40s that we get a real sense of who we are as people."

Whether we're picking a career at age 18 or at age 48, most of us want to do something we love. Unfortunately, we often confuse ability with passion: I'm good at math, so I should be an engineer. I'm very persuasive, so I'll be a natural in sales. Warns Parachute author Dick Bolles: "The assumption we've made in our culture is that because you do something well you must love it. Well, efficiency and love are not the same thing."

Yet the notion that you can let passion be your guide--the standard line of advice in many books about careers--turns out to be not all that realistic if you're contemplating a change of vocation in midlife. To be sure, some intrepid adults do take off in wanton pursuit of their occupational fantasies and succeed. At age 35, Paul Gauguin, a Parisian financier, left his job and ended up painting voluptuous women on Tahiti. (For profiles of three others who made a radical midcourse correction, see the following story.)

Shifting to a new career rarely turns out to be the sort of apocalyptic, burn-the-bridges, run-off-to-Seattle-with-your-mistress experience that some might expect. Says Maureen Shiells, a counselor at the Career Action Center in Palo Alto: "People often assume that everything is wrong; that they'll have to throw everything away, start all over again, go back to school, go into debt, learn a whole set of new skills."

But changing careers is not really about dramatic change. It's about continuity, about translating your experience and your expertise into transferable, marketable skills. You're a sales rep who's longed to become a teacher? Well, have you ever mentored a younger employee? You're a teacher who's eager to get into marketing? Okay, haven't you had to sell children and their parents on the importance of education?

CHANGING CAREERS is also about compromise, and compromise is something most middle-aged folks are pretty good at. Any boomer contemplating a shift is going to have to wrestle his way through a series of gnarly dilemmas involving work, money, family, status, and time.

Those issues loomed large for Ron Sheade when he set out to reboot himself professionally three years ago. He had been a lawyer and manager at Comdisco, a leading computer-leasing company, for 12 years when he lost his job in a round of reengineering. His boss offered him a choice: another position with similar responsibility but lower pay or early retirement with a generous severance deal and as much outplacement counseling as he needed. Sheade took the package--and started looking for a new job in corporate America, just like the one he had left behind.

But two months into the search he had an epiphany. Says he: "I just didn't have any enthusiasm for what I was doing. I began to realize, with hindsight, that I had been on a treadmill for a very long time, that my vacations often got interrupted because of a crisis at work, that I wasn't at home all that much, and that when I was at home I was there physically but not mentally."

So Sheade decided to go home again, in more ways than one. He became a teacher, a profession he had pursued 15 years earlier, before he entered law school. Two years ago he accepted a job as a junior high school teacher in Wilmette, the same Chicago suburb where he had taught in the 1970s. As a teacher, Sheade has rediscovered the kind of close collegiality that he never found in the corporate world. He has also reconnected with his family. He rushes home from school four days a week to care for his two daughters, ages 6 and 11. His wife, Gina, who had put her career on hold to raise the kids, now pursues a master's degree in library science.

And what of the downside to this kind of change? To accommodate a precipitous plunge in their annual income, the Sheades have had to downscale their lives. They moved out of the showcase house they had lived in for just 18 months and sold their vacation home in Indiana. A hawk with a Hewlett-Packard calculator, Ron watches over his finances, which he must stretch into three college tuitions (counting Gina's) and two retirements. He has invested some of his legacy from Comdisco conservatively, mostly in Treasury bills and Illinois bonds.

Difficult as it is to change careers when you've lost your job, there's one thing that's even harder: changing careers when you haven't lost your job, when there's no clear necessity to make such a dramatic move.

BY ALL APPEARANCES, Audrey Struve was doing excellent work as a project manager in charge of relocation at Raychem, an electronics manufacturer in Menlo Park, California. During seven years on the job, she earned steady promotions and regular raises, even as people elsewhere in the company were being laid off. But she was secretly unhappy: "I felt anguished. I was doing really well, getting tremendous evaluations. My customers liked my work. But I was miserable. And I didn't know why. I thought something was desperately wrong with me."

A year ago, Struve, a soft-spoken woman with shoulder-length blond hair and large, round-rimmed spectacles, began working with a counselor in Raychem's career center. She walked into the center complaining about stress and overwork. That's hardly surprising. Counselors say that most clients come in saying they hate their boss or they don't like their commute or they consider their co-workers cretins. But Struve's real problem, she soon realized, was that her job didn't match her personal values, her need to do something that she considered socially significant.

With the help of books, psychological tests, software, and other tools, Struve came up with a list of her accomplishments and abilities and the attributes she wanted to find in her next job. Her ideal setting, she determined, would be a small, nonprofit organization involved in social service. She reasoned she could take her skills as a project manager into a new arena. Says she: "Once you've figured out what you believe in and you've thought through what you can do, then selling yourself to a potential employer is easy."

Just ten days after Struve began combing through a computerized list of job openings in the Bay Area, she was hired to become a project coordinator at the American Institutes for Research, a nonprofit group that conducts education research nationwide. Struve, who's about to turn 40, now has an occupation that fits her values. Says she: "This feels immensely better. I'm a changed person. I make less money, but that's okay. What I'm doing now helps better humankind."

People who change careers rarely do it in one giant leap. Jacqueline Silveira, 35, lost her job a year ago as a facilities planner at Sun Microsystems when the company outsourced her entire department. But her career-changing odyssey actually began long before that.

A native of Mexico who had studied architecture, Silveira, 35, drifted into facilities planning because she knew how to draft a blueprint. Three years ago she peered into her future, and it seemed boring: "I looked at all the positions I could ultimately hold, and none of them were fun or exciting." So she set up a series of "information interviews," discussions with Sun managers about jobs that might allow her travel back to Latin America. They convinced her, a nontechie, that she needed better business skills if she was going to prosper in Silicon Valley. So she enrolled in an MBA program at a nearby college, taking classes two evenings a week for three years.

An outgoing woman who favors brightly colored clothes, Silveira figured she'd be well suited to international marketing. Although she had never held a formal marketing position, she did have experience dealing with tough customers, the 1,700 Sun employees served by her facilities department. Five weeks after she lost her job, Silveira landed a new one, as a domestic marketing rep in Sun's rapidly growing software business. She now hopes her next position, perhaps three or four years from now, will get her overseas. Says she: "I want to learn everything I can about marketing first. My plan is to crawl before I can walk."

Changing a career is never easy. It takes time, and you may make some wrong turns. But if you feel you need to do it, then you probably do--and probably should. Managed well, a career shift in midlife makes you feel like you've got the keys to the car, a date for the prom, and a chance, once again, to pursue your dreams.

Reporter Associate Ani Hadjian