Blood samples were collected from patients attending clinics for sexually transmitted diseases (STDs) and antenatal clinics, as well as from voluntary blood donors in government hospitals from December 1989 to March 1993 in Madras, Tamil Nadu. The samples were collected once a week on a selected day from 20 patients coming to the clinics. ELISA test was performed using Virnostika Mixt Kit and seropositive samples were confirmed by Western blot. The percentage of seropositivity was compared for each 6-month period for the 3 categories. There was an increase in the incidence of HIV infection in all 3 population categories. In STD clinic attenders the increase in incidence was 10-fold (1% March 1990 to 10% March 1993). In the antenatal clinic attenders the increase in incidence was 2-fold (0.37% September 1990 to 0.76% March 1993). In voluntary blood donors the increase in the incidence was 3-fold (0.24% March 1991 to 0.72% March 1993). The 10-fold rise in the incidence of HIV infection in STD clinic attenders is attributable to their sexual practice involving multiple partners. But the steady increase in the incidence for the 2 low-risk categories (2-fold rise in antenatal mothers and 3-fold rise in voluntary blood donors) clearly shows that the HIV infection no longer spreads only to people with high-risk behavior, but has trickled into the general population as well. The first seropositivity in mothers attending antenatal care was recorded in June 1990 and in voluntary blood donors in January 1991. Since then there has been a steady increase in the incidence of HIV infection. The data have generated valuable information for the planning and evaluation of control programs, demonstrating that AIDS awareness/prevention programs should be targeting all people. Over time, sentinel surveillance by way of anonymous unlinked HIV testing will provide an accurate assessment of prevalence and will improve the estimate of the impact of the epidemic in the entire population.