The service helps locate a young, affluent demographic increasingly hard to reach via radio and television. "It's an incredibly simple interface: Plug in which audiences you want to reach, choose specific podcasts, track your budget and your campaigns, and upload ads," says Murgesh Navar, CEO of Mountain View, Calif.-based Podbridge. "Advertisers pay for information. Content providers get a share. Everyone gets information on who's listening, how often," he says.

Podbridge ensures that a show downloaded on Friday but listened to on Wednesday, or even a month later, has new ads tailored by demographic. Advertisers and shows can choose each other, allowing podcasters to ban cigarette ads, for instance.

While it's unclear how profitable it is to advertise on podcasts, Podbridge has distribution agreements with such players as Sporting News Radio, BBC Radio, and Clear Channel.