Unlikely Model for H.I.V. Prevention INDUSTRY DATABASE Shylar Cobi, right, a film producer, confirmed test results of the actors who perform as James Deen and Stoya. LOS ANGELES - Before they take off all their clothes, the actors who perform as James Deen and Stoya go through a ritual unique to the heterosexual adult film industry. First, they show each other their cellphones: Each has an e-mail from a laboratory saying he or she just tested negative for H.I.V., syphilis, chlamydia and gonorrhea. Then they sit beside the film's producer, Shylar Cobi, as he checks an industry database with their real names to confirm that those negative tests are less than 15 days old. Then, out on the pool terrace of the day's set - a music producer's hilltop home with a view of the Hollywood sign - they yank down their pants and stand around joking as Mr. Cobi quickly inspects their mouths, hands and genitals for sores. "I'm not a doctor," Mr. Cobi, who wears a pleasantly sheepish grin, says. I'm only qualified to do this because I've been shooting porn since 1990 and I know what looks bad. Bizarre as the ritual is, it seems to work. The industry's medical consultants say that about 350,000 sex scenes have been shot without condoms since 2004, and H.I.V. has not been transmitted on a set once. Outside the world of pornography, the industry's testing regimen is not well known, and no serious academic study of it has ever been done. But when it was described to several AIDS experts, they all reacted by saying that there were far fewer infections than they would have expected, given how much high-risk sex takes place. "I don't think there's any question that it works," said Dr. Allan Ronald, a Canadian AIDS specialist who did landmark studies of the virus in prostitutes in a Nairobi slum. I'm a little uncomfortable, because it's giving the wrong message - that you can have multiple sex partners without condoms - but I can't say it doesn't work. Despite the regimen's apparent success, California health officials and an advocacy group, the AIDS Healthcare Foundation, are trying to make it illegal to shoot without condoms. They argue that other sexually transmitted diseases are rampant in the industry, though the industry trade group disputes that. In January, the city of Los Angeles passed a law requiring actors to wear condoms. A measure to do the same for the whole county is on the ballot on Tuesday. Producers say the condom requirement will drive them out of business since consumers will not buy such films. Local newspapers like The Los Angeles Times oppose the ballot measure, calling it well-intentioned but unenforceable, and warning that it could drive up to 10,000 jobs out of state. Very frequent testing makes it almost impossible for an actor to stay infected without being caught, said Dr. Jacques Pepin, the author of "The Origins of AIDS" and an expert on transmission rates. And if you are having sex mostly with people who themselves are tested all the time, this must further reduce the risk. When the virus first enters a high-risk group like heroin users, urban prostitutes or habitués of gay bathhouses, it usually infects 30 to 60 percent of the cohort within a few years, studies have shown. The same would be expected in pornography, performers can have more than a dozen partners a month, but the industry says self-policing has prevented it.. "Our talent base has sex exponentially more than other people, but we're all on the same page about keeping it out," said Steven Hirsch, the founder of Vivid Entertainment, one of the biggest studios. Performers have to test negative every 28 days, although some studios recently switched to every 14. If a test is positive, all the studios across the country that adhere to standards set by the Free Speech Coalition, an industry trade group, are obliged to stop filming until all the on-screen partners of that performer, all their partners, and all their partners" partners, are found and retested. In 2004, the industry shut down for three months to do that. It has had briefer shutdowns in each of the last four years. In 2009 and 2010, no other infected performers were found. Coalition representatives said an infected woman in 2009, from Nevada, may have had an infected boyfriend, and offered evidence that a man infected in 2010 in Florida had worked outside the industry as a prostitute. The 2011 test was a false positive. A shutdown in August came after several actors got syphilis, not H.I.V. All performers were given a choice: Take antibiotics, or pass two back-to-back syphilis tests 14 days apart.