(FORTUNE Small Business) – It has been spotted in the Denver Broncos locker room. And those of the Boston Celtics, New York Yankees, and San Francisco 49ers. It is Flex-Power, a new joint- and muscle-pain-relief cream that has gotten into the hands (and on the bodies) of some of the biggest names in sports and entertainment, including athletes from close to 50 professional and major college basketball, football, and hockey teams.

Yet while the product's reputation may be big, the company behind it--Berkeley-based Flex-Power--is small. Total employees: eight. Sales in its first year of distribution: $100,000. Its founders, Bejan Esmaili, 39, and Rasheen Smith, 27, do not collect a salary. But now Esmaili and Smith are engaged in an ambitious plan to pump up their company. Can it become the Gatorade of sports creams? Or will its moneyed competitors like Bengay (owned by Pfizer), Icy-Hot (Chattem), and Mineral Ice (Bristol-Myers Squibb) keep them out of the game?

For Flex-Power to succeed, it needs to pull off a transition that might seem backward: Having succeeded in the world of professional sports, the company must now win approval among the amateurs--the same strategy that once worked for Gatorade and PowerBar. To accomplish that, Flex-Power introduced an advertising campaign in October 2003. The first TV ads appeared in the Bay Area and featured testimonials from 49ers running back Garrison Hearst and offensive linemen Jeremy Newberry and Ron Stone. (Hearst and Stone are no longer with the team.) Over the course of this year, the company plans to introduce ads in other markets, featuring such boosters as baseball legend Hank Aaron (who uses the cream when playing golf) and the New Jersey Nets' Jason Kidd. In March, Flex-Power--which was available only via telephone or the Internet--went on sale on QVC. By the end of the third quarter, Esmaili and Smith hope to have their product in stores.

Flex-Power was born in 1999, when Esmaili--a former soccer player for U.C. Berkeley who still plays in a local league--needed knee surgery. Afterward he turned to typical sports creams for relief but couldn't abide the way they smelled, reeking under the suits the Morgan Stanley executive wore to work. (Esmaili managed money for several professional athletes.) At the same time Esmaili was wary of prescription pills. Many professional athletes would share his concern by 2000, when Alonzo Mourning, then center for the Miami Heat, was diagnosed with focal glomerulosclerosis, a kidney disorder. Medical experts say that oral anti-inflammatory medicines did not cause his disease. But the caveat that excessive use of such drugs--from over-the-counter medications like ibuprofen and aspirin to prescription drugs like Vioxx and Indocin--can in rare cases lead to other kidney problems was enough to scare many athletes.

The fear unleashed by Mourning's disease may have been bad science, but Esmaili thought it could be good for business. He asked Smith--whom he'd met through a mutual friend--to pen a business plan. In August 2000 the two founded Flex-Power with $500,000 raised from family and friends, and with an idea: to create a topical sports cream made with methyl-sulfonyl-methane (MSM) and glucosamine--anti-inflammatories that had previously been taken orally--that didn't stink.

They hired a team of scientists, who took two years to develop a formula. Unable to afford market research, Esmaili and Smith combed health and beauty aisles of local drugstores, sniffing products in search of a scent. They enlisted the guidance of PowerBar founder Brian Maxwell, who advised them to start with two varieties of the cream to meet wider demand. (Customers have a choice of Clean Scent and Citrus Light.) They also ran early trials by some of Esmaili's former clients on the 49ers, who advised them to add a heating sensation. (Off-the-shelf anti-inflammatory creams usually heat or cool an affected area. Though soothing, neither effect is a result of active ingredients.)

The resulting product does indeed smell good. And athletes seem impressed with the way it soothes their muscles, even though--like all sports creams--its medicinal qualities are questionable. (Topical anti-inflammatories require no FDA approval.) "Does it work because of the medication? Or does it work because you are massaging your muscle with a soothing cream?" asks Warren Strudwick, team doctor for the Oakland Raiders, who has given Flex-Power to players. "Who knows? It doesn't really matter as long as there is some relief."

Esmaili's contacts in the sports world helped get the cream into locker rooms. Now Esmaili and Smith hope they've earned the cachet to go after the $273 million market for topical analgesic creams. "We are hoping for a trickle-down effect," Esmaili says. "Athletes don't corner the market on aches and pains."

Indeed, Smith has already suffered enough pain for an entire team. Raised in South Central Los Angeles in a house filled with drugs and alcohol, Smith met Esmaili during his first year of Cal Berkeley through a mutual friend. Esmaili quickly became Smith's mentor, showing him the ropes of his alma mater. Now the two friends finish each other's sentences like brothers. "We are like family, and this is a family business," says Smith.

And it's a family business that--despite its mission to eradicate all forms of muscle aches--may be about to meet the one type of pain it truly likes: growing pains.