(FORTUNE Small Business) – WHAT DOES THE TERM 'PUBLIC RELATIONS' CONJURE UP in your mind?" asks David Fenton, the tall, gray-haired, blue-eyed, 51-year-old founder of Fenton Communications. We've only just shaken hands; I haven't even sat down. Before I can object--hey, I ask the questions!--he answers, "Something unethical. It means, 'Will lie, distort, say anything for money.'" He said it, not me.

I'm in Fenton's unflashy Manhattan office, a satellite of Washington-based Fenton Communications, the country's leading social-advocacy PR firm. Social-advocacy PR is an industry subgroup that didn't exist until 1982. That's when Fenton--a '60s radical, an Abbie Hoffman protégé ("He was partially crazy but he was very brilliant"), and a former flak for Rolling Stone magazine--sensed that the "nexus of politics and communications" was where it was at and decided that "there should be a PR firm that worked for values, ethics, the environment, human rights, and public health." So he started one.

"We are trying to use communications to make the world better, and we happen to have a business doing that," says Fenton, whose 40-person shop billed about $6 million in 2002 (roughly 20% off its pre-9/11 peak). He doesn't tout products so much as causes, unless the products themselves are draped in causes. Among his clients: Ben & Jerry's, the Body Shop, the Solar Industry Energy Association, and Nelson Mandela. Recently it was Fenton, working for the Evangelical Environmental Network, who produced that catchy "What would Jesus drive?" anti-SUV campaign. And it was Fenton, on behalf of Arianna Huffington's Detroit Project, who ran those cheeky TV spots linking people who drive big cars to financial support for Osama bin Laden's terrorist network. Another client, ISP provider ManyOne Networks, is in business, says Fenton approvingly, "to try to divert all the money that's going to AOL Time Warner [parent of FSB's publisher] and Bill Gates to social change."

Okay, but what about all the money that's going to Fenton? Radical pedigree aside, he's got nothing against good old American business. Like Paul Hawken, Anita Roddick, and Ben Cohen, Fenton hopes to "make money by doing good things." Actually, he'll go even further. Some problems--like ecological disaster--can be solved only by business. As he puts it, "The products have to change. Who else is going to change them?"

Pretty convincing--until you remember this guy's in PR. Is he just spinning his career the way he'd spin a product? Fenton insists not: "We take on only things that are true and that we believe in, and we won't spin or distort or put out misinformation under any circumstances, even if we believe in the causes for which we would be asked to do that." Which is great, if you ask me. Noble, even. For the first time in my life, I'm trying my hardest to believe a flak.