Adam Bold has always dreamed of building a successful business. Becoming wealthy? Yes. Acclaim in his industry? Absolutely. Being recognized in the supermarket? Not so much. And yet Bold, founder of the Mutual Fund Store, a franchise of investment and asset management offices based in Overland Park, Kansas, is stopped daily by someone who recognizes his name or voice. "I'll go to a party now, and people think they know me; they want to talk to me all night," says Bold. "It's certainly given me a new perspective on the whole Lindsay Lohan thing."

Bold owes his budding fame in large part to his second career: He hosts The Mutual Fund Show, a weekly finance radio show that has four million listeners in 51 cities. Given that success, Bold was cast as the host of a new television program, which debuted on Kansas City, Missouri's PBS affiliate in the fall.

Bold considers the radio show the highlight of his week--and not just because it feeds his ego. The program has given his company greater visibility than he ever thought possible. Revenue in 2007 will hit $24 million, an increase of 31 percent since 2005, when Bold's radio show went national. (Systemwide, the Mutual Fund Store's 63 offices will gross almost $45 million this year.) Much of that growth, Bold says, can be attributed to the exposure he has received on the radio.

Ten years ago, a show devoted solely to mutual funds might have seemed too much of a niche play. But in today's thousand-channel universe, the niche market has become the norm. "There's been a great opportunity for people with specific topics to go on the air," says Laura Smith, program director at Lime, a Sirius Satellite Radio (NASDAQ:SIRI) channel devoted entirely to green living. "There's a place for everything right now."

Entrepreneurs, with their smooth sales spiels and, in many cases, specialized expertise, are well placed to satisfy the hunger for new shows. Hosting an original program is a great alternative to paying for a commercial or an infomercial. First of all, it's cheaper. And it may well be more effective. "It's all about credibility," says Tom Himpe, author of Advertising Is Dead: Long Live Advertising! "Advertising messages have low credibility, so brands have to infiltrate programming in order to appear unbiased."

Call-in and talk show formats can be especially effective, because they let a business owner demonstrate knowledge of a subject. On his hourlong radio show, Bold fields questions about mutual funds and other investment options. He got his break on air in 1997, shortly after opening his first store in Kansas City. Peter Newman, a local accountant with whom Bold shared some clients, invited him to appear as a guest on a weekly finance program on KMBZ-AM. "I had never been on the radio before, but I thought, Why not?" Bold recalls.

The two hit it off, and Bold began appearing roughly every other week for the next two years. He filled in as guest host when Newman went on vacation. With cassettes of his radio work in hand, Bold eventually got up the nerve to approach the program director, asking if he could host his own mutual fund-focused show. He was initially rejected, but by 1998 he had managed to get his own show on Saturday mornings.

The program has seen such steady audience growth over the past nine years that last year, PBS came to him to put together a TV spinoff. Because of public broadcasting rules, Bold won't be able to direct viewers to his company's website or mention its toll-free phone number, which he does three times during each radio broadcast. But Bold says that's no big deal, adding that marketing "is not something I think about while doing the show."

By contrast, Michael Salzhauer, who has a plastic surgery practice in Bal Harbour, Florida, is much more aggressive when it comes to turning members of his show's audience into paying customers. Salzhauer hosts a weekly call-in show called Nip Talk on WINZ-AM in South Florida, on which he answers questions about subjects as diverse as breast implants and Botox injections. He expects to close the year with $3 million in revenue, $1 million more than he made last year before he went on the radio. Half of that increase came specifically from customers who identified themselves as his show's listeners.

As part of his arrangement with the station, Salzhauer gets a block of four minutes of commercial advertising. Typically, he resells half of that time and uses the other half to advertise his practice. He also offers frequent promotions, like trivia contests, through which listeners can win prizes, including free consultations and free laser treatments. "This gets people in the door, and they'll usually go on to purchase another product at some point down the line," says Salzhauer, who says he'd recommend broadcasting to "any business--especially service businesses where people are really experts in what they do."

Broadcasting is not as easy as showing up and talking, of course. Unless you are a natural in front of the camera or the microphone, it takes a lot of training to be comfortable and convincing. Bold spends at least 20 hours a week preparing for his radio and TV shows, and he actually stepped down as CEO of his company this spring in part to spend more time on media.

Something else Bold has had to get used to as a national radio host is that the higher profile comes with higher stakes for him professionally. He's now giving investment advice to millions of people. Every segment could have an impact on his reputation. "If I make a bad recommendation on my show, everybody knows it," he says. "That's a lot of pressure."

Josh Dorfman, another entrepreneur who moonlights as a broadcaster, also spends about half of his week preparing. Dorfman hosts The Lazy Environmentalist, a Sirius Satellite Radio show that airs on Lime every weekday morning at 11. Dorfman is the founder and CEO of Vivavi, a Brooklyn, New York, company that sells ecofriendly furniture. Vivavi did $1 million in annual sales in 2007--double what it brought in last year.

Dorfman's road to radio started with a blog about green living that he began in 2005. Then he started doing an Internet radio show and wrote a book, which led him to Sirius. Today, the company spends very little on formal marketing, relying on the broadcast to promote itself. "Customers come into the show room and say 'I love your radio show' or 'I read your book," Dorfman says. "The more people have come to recognize me as a voice in the industry, the more Vivavi has grown."

Dorfman is also able to use the radio show to go after corporate accounts. When a developer unveiled plans to erect a certified green high-rise on New York City's Roosevelt Island, Dorfman invited him on the Sirius show, which helped to secure a contract for Vivavi to sell furniture for the building's outdoor area. "My approach is not quid pro quo, because I'd have many of the guests on anyway," says Dorfman. "But this way we can both deliver value to each other."

Correction: The original version of this story, which appeared in the December 2007 issue, misidentified the name of Adam Bold's radio show.