(FORTUNE Small Business) – Judging by the huge white bandage plastered on his forehead, the Continental Airlines employee in his blue-and-gold epauletted shirtsleeves needed some medical attention. But he was lucky. Because the walk-in clinic he was visiting was right at Newark Liberty International Airport, chances were good he would receive care and be back at work quickly. In addition, the clinic staff would check him for problems such as high blood pressure and diabetes and get him started on any treatment he might need. His out-of-pocket cost? Zero.

The clinic is one of dozens run by Whole Health Management, a small, Cleveland-based company that operates on-site medical clinics and fitness centers and provides preventive-care services for large employers as diverse as Nissan, Sprint, and the U.S. Nuclear Regulatory Commission. On-site medical clinics have been around for decades--remember the company doctor?--but employers are rediscovering them these days as they struggle to contain rising health-care costs. "This area is exploding in terms of corporate interest," says Dr. Alan Spiro, the head of health-care-management practice for Towers Perrin, a consulting firm based in New York City. "It's a back-to-the-future phenomenon."

But not all the way back, at least as Whole Health approaches its task. In the old days on-site clinics' primary function was to treat on-the-job injuries. But at Whole Health clinics, employees are as likely to get counseling on quitting smoking as they are to get advice on their stitches. "Their philosophy is to look at the person's whole health," says Pat Claiborne, senior manager of medical programs for Continental. "That broad approach is part of why they deliver such a good product."

Every dollar a client invests in Whole Health Management returns $3, says James J. Hummer, president and chief executive officer, who founded the company in 1987. Those savings are calculated based on both direct medical costs and indirect costs such as lost work time. But Bruce Kelley, a senior consultant for Watson Wyatt Worldwide, which helps companies analyze whether contracting with such companies as Whole Health Management will save them money, says a three-to-one return may be too optimistic. Among other factors, it is hard to predict how many employees will use an on-site clinic instead of going to their regular doctor, he says.

Still, many clients voice enthusiasm for Whole Health. The firm's annual revenues rose from $5 million in the mid-1990s to $15 million at decade's end. This year Whole Health is on track to produce $30 million in revenue. While customers are most interested in saving money on health care and workers' compensation, Whole Health execs insist that cutting costs for clients is not the company's top priority. "If we focus on getting employees healthy, then we know that the financial outcomes will follow," says Hummer.

Financial services company Freddie Mac opened an on-site medical clinic for more than 4,000 employees at its McLean, Va., headquarters last fall. Whole Health Management runs the clinic. Freddie Mac's mostly white-collar workforce of investment, software, and sales professionals is unlikely to suffer on-the-job injuries. Instead the clinic focuses on employee wellness, with screenings for high blood pressure, cancer, and other chronic conditions such as asthma.

At the very least, the company expects to drastically reduce the typical two hours employees take off for a doctor visit. But there are even higher hopes. "This is an incredible opportunity to bring wellness to Freddie Mac," says Mike Hager, senior VP for human resources for the company. "We believe it will have a huge return as well as increase the engagement of employees in their jobs." Of course, an on-site clinic is no miracle. But amid the tangled issues of workplace health care, every little bit helps.