(FORTUNE Small Business) – After he had driven four hours to buy a wheel-chair that would allow him to play tennis--and was ignored by the salespeople at the company that made it--John Box was so angry that he decided to do something about it. When Box returned home, he and a brother, both engineers, teamed up to invent their own athletic-oriented chair. Box was soon marketing it at the wheelchair tennis matches in which he competed around the country. That was in 1992. Today Box, 41, sells eye-catching high-performance wheelchairs designed for everything from downhill racing to hockey. The chairs cost $1,500 to $3,000 apiece, allowing his firm, Colours Wheelchair, to turn a profit on more than $2 million in annual sales.

Colours, based in Corona, Calif., gets many of its design ideas from employees who use wheelchairs and also from 75 wheelchair athletes it sponsors around the world. "The only obstacle to doing anything is this little word called 'determination,'" says Box, who became a paraplegic as a result of surgery following a motorcycle accident when he was 17. "Once somebody is determined to do something, it's all downhill."

Box has raised eyebrows--and perhaps sales--with an advertisement for Colours that features a pregnant woman, half covered by a denim shirt, who uses a wheelchair, as well as another disabled woman in sexy lingerie, lying on her back in a wheelchair that has been tipped over. Even the names of his wheelchairs, which range from the Hammer, a model used for contact sports, to the Spazz, for everyday use, have an edge. Box says his Christian faith has allowed him to appreciate the compensating gifts that his disability has brought him, and he sees changing public perceptions of people with disabilities as part of his company's mission. "We're trying to educate people that having a disability doesn't change your personality," says Box, who, when he's not playing wheelchair sports, likes to race off-road vehicles in the desert.

As Box has discovered, making it possible for others with disabilities to pursue their passions is good business. The U.S. Census Bureau counts nearly 50 million Americans, or 17% of the population, who are at least 5 years old and are disabled, which it defines as having a condition that limits work, education, or another major activity. Those with extreme conditions--paralysis, blindness, cognitive challenges--account for no more than half of this group, according to federal experts. The rest suffer from afflictions such as arthritis and asthma. All are in the market for products and services that help them enjoy life more fully. Collectively they spend $796 billion a year on everything from rent to vacations, according to the most recent estimate by Packaged Facts, a New York City market research firm. "Don't go after this market because it's the right thing to do; go after it because you want to make money, and the rest will follow," says Carmen Jones, president of the Solutions Marketing Group in Arlington, Va., which helps companies target customers with disabilities.

More than a quarter of all disabilities strike Americans who are 65 and older, and with the huge wave of baby-boomers approaching that age, the rewards of reaching out to disabled customers soon will swell dramatically. "Boomers are not aging gracefully," says Joan Stein, president and CEO of Accessibility Development Associates, a Pittsburgh firm that helps businesses comply with the Americans With Disabilities Act. "We're not willing to live with inconveniences that our parents may have been willing to live with."

To give businesses a better handle on the spending habits of consumers with disabilities, Nielsen National Research Group Independent in New York City recently embarked on market research initiatives with EIN SOF Communications, a Los Angeles marketing and public relations firm that specializes in campaigns related to disabilities. Nielsen recruited two focus groups of Americans with spinal cord injuries, one of which also included family members, to see how they perceived particular products and brands. It provided confidential data to the companies that participated. Other data will be used as the basis for a national report card for businesses, rating them on how well they accommodate consumers and employees with disabilities. The National Spinal Cord Injury Association expects to announce its report card later this year. Nielsen and EIN SOF Communications are now setting up similar focus groups among consumers who are blind, deaf, and hard of hearing.

Open Doors Organization, a Chicago-based social action research group for Americans with disabilities, will soon offer to provide companies with mystery shoppers who have disabilities, so that the firms can learn to better serve their disabled clientele. Open Doors says it will soon report the results of a study done with the Travel Industry Association of America, which reveals that Americans with disabilities spent an estimated $14 billion on travel in 2004, up from $13.6 billion in 2003. The fastest-growing category was trips within Canada and Mexico. "People with disabilities want to travel, and when they travel and have a good experience, they are likely to travel again," says Thomas Zoeller, a vice president of the American Association of Airport Executives. "It's certainly a community with a lot of disposable income. There's a lot of word-of-mouth about good hotels, good businesses. And individuals with disabilities tend to travel with someone else. This market has not been fully tapped."

Avis Rent A Car would agree. It saw sales to customers with disabilities jump by 30% over two years after it introduced five devices to make its rental cars more accessible, such as a transfer board that lets drivers move from their wheelchairs into their vehicles. Michael Caron, a vice president at Cendant Car Rental Group, which owns Avis, says of the investment, "The reward far outweighs the expense." Cendant is now rolling out the program across the country at another of its car-rental companies, Budget Rent A Car.

Even firms that are a fraction the size of Cendant can benefit from becoming friendlier to the disabled, says Adrian Guglielmo, president of Diversity Partners, a marketing firm in Brewster, N.Y., that worked with Avis on its campaign. Many big firms are looking for small suppliers that help them achieve their diversity goals, which include hiring and marketing to Americans with disabilities. "If you're a printer and employ three or four people who are deaf, tell the big companies," says Guglielmo. "If you invent a product, and you make sure it's accessible, that's a niche for you."

The Justice Department, which plays a leading role in enforcing the Americans With Disabilities Act, is reaching out through a program called the ADA Business Connection to small businesses that want to attract more disabled customers and employees. It is introducing small-business executives to heads of organizations that represent Americans with disabilities. "More than 97% of the employers in the country are small businesses," says Ollie Cantos, a special assistant at the Justice Department. "We especially want to work with small businesses because those are the ones people go to everyday."

In the pages to come, we have identified small companies--some owned by disabled Americans--that have found smart ways to appeal to disabled customers and hire disabled employees. We also sort through the confusion surrounding what the law requires small companies to do to accommodate disabled workers and customers, a source of considerable frustration among even the most well-intentioned business owners.