OFFERING sex for money (solliciting) is illegal in Senegal, but having sex for money is not. In th is mostly Muslim African country, a sex worker may ply her trade as long as she is registered as a prostitute, has regular check-ups at a designated clinic and is discreet. Dakar, Senegal's capital, is one of the commercial sex capitals of Africa, with prostitutes coming from all over the sub-region as well as the Middle East. Why then does Senegal have one of the lowest number of AIDS cases in Africa -- less than 3,000, in a population of 8.3 million? The World Health Organisation (WHO) says that legalising prostitution is part of the reason. Senegal's government has been registering sex workers since 1966 -- long before AIDS was ever heard of -- to combat sexually transmitted diseases (STDs) like Syphilis andGonorrhoea. Researchers agree that reducing STDs also reduces the rate of HIV infection. Each day, women crowd the clinic in downtown Dakar. "If you have yellow fever, if you have any little diseases they will tell you," says a woman who gave her name as Sarah. "Sometimes they even give drugs for free. Otherwise you must buy them, or they will not stamp your card." Registering does have its downsides. Sarah complains that police can harass her whether or not her card is up to date "And if you decide you no longer want to be a prostitute the de-registration process is slow if not impossible," she says. Still, it's worth it if the result is less AIDS. Problem is, many experts are not convinced that registering is the reason. Michael Tardy, who runs the Dakar clinic, admits that only about a quarter of Dakar's professional prostitutes register. "The rest work clandestine." Many women have sex for money in this society, she says. "Most don't recognise themselves as prostitutes." Some experts still see a logic for why AIDS levels are low. El Hadj Sy, co-ordinator of health programs for the NGO, Enda-Santi, says 'informal' sex workers often have only a few clients who become de facto husbands. At the same time, he points out that polygamy is common. Men may legally marry up to four wives. "None of these people get check-ups, either," he says. While Senegalese may have multiple partners, Sy denies that means they are promiscuous. "People have sex in clusters," he says. Body fluids are only exchanged amongst a limited number of people. "In a polygamous household, if the man and his wives do not sleep with other people there is no way to get infected," he argues, adding that "culture and religion are a strong social control." Others are not so sure. For Kate Cisse Wane, head of the nation program on AIDS, "claims that because this is a Muslim country people have sexual behaviour different from the sexual behaviour of other African countries are questionable." Sex workers in the villages often travel to the big cities or follow migrant workers, says Wane. "They then have sex with many men." As for polygamy, Wane notes that when married men are searching for second or third wives they invariably "try out" lots of other women. And, she notes, "Senegalese men are often looking for second or third wives." So why then are only 70,000 serpositive people -- less than two percent of the population -- in all of Senegal, while in nearby Abidjan the level is 15 percent? "We simple don't know," says Tardy. Most astonishingly, while 15 percent of the professional sex workers that come to the clinic are infected with the HIV, that level has not increased since 1992. There are still many theories. Soulyman Mboup, a professor at Dakar university, has shown that the HIV 2 virus (which he discovered) is common in Senegal -- it is both less virulent and less contagious than HIV 1. But there are also no clear answers as to why the type 2 virus is common here when sex workers come from all over Africa and why HIV 2 is common in other regions where AIDS levels are high. Western experts continue to stress the importance of legalising sex work. That way, they say, sex workers have been able to develop a 'code of conduct' to ensure that their clients use condoms. "If you tell a man that you won't have sex without a condom he can't just go to the next corner and find a sex worker who will," says one sociologist. Yet according to sex workers themselves, some Senegalese men also insist on not using condoms. In a discussion group at the clinic, women complained that they do not have the power to enforce: "The Senegalese men say 'I am not sick. Are you sick?... Then why do we need it'?" El Hadj Sy remains convinced that there are "indigenous strategies" for minimising the risk of infection. Traditionally in many parts of Senegal, when a man dies his brother marries the widows and AIDS experts have long believed that when the death is AIDS related the HIV virus is then automatically spread to the brother and his first wives. But according to Sy, village elders are becoming aware of this risk. "In some villages they have changed the practices so widows must come and sit on the lap of their brother-in-law, but they no longer have to marry or have sex with him," he says. Still, Sy admits he doesn't know which are the strategies that are most significant in keeping AIDS levels low. Next year a study will be conducted in both Senegal and Uganda -- a country with one of the highest incidents of AIDS. "Hopefully then we will know which factors count," he says.