To determine the prevalence of HIV-1 antibody and risk factors associated with a positive test in a heterosexually promiscuous female population, we initially screened 412 prostitutes in remand homes in three cites and three towns in Tamil Nadu state (southern India) and then tested all new entrants to one home in Vellore from 1986 to 1990. The proportion of women infected (10 of 102) from the port city of Madras was greater than from all other cities or towns combined (four of 310, p = 0.0002). The only significant risk factor for development of HIV-1 antibody was exposure to foreigners (odds ratio: 7.71; 95% confidence interval 4.2-11.2; p = 0.0004), after correcting for the influence of city. In Vellore the prevalence of HIV-1 antibody increased from 1.8% in 1986 to 28.6% in 1990, with a doubling time of 0.95 years. We hypothesize that HIV-1 infection has been introduced into India relatively recently into the heterosexually promiscuous population, where there has been some spread. Preventive measures should be urgently directed toward this population to prevent spread in the general population.