We studied the sensitivity of polymerase chain reaction (PCR) for detecting early human immunodeficiency virus-1 (HIV-1) in sex workers. Blood samples of sex workers who attended our Sexually Transmitted Diseases clinic were tested for HIV infection by testing for the presence of HIV antibody and HIV-1 proviral DNA using PCR (with the Amplicor HIV-1 amplification kit, Roche) at 00 (when they first register to work as sex workers), 01 and 03 months after starting work. The objective was to detect HIV-1 using PCR in sex workers during the "window" period when their HIV antibody tests were still negative. Sixty-nine blood samples were PCR-tested at 00 month of which 8 were simultaneously positive for HIV antibody and PCR tests. Seventy-seven blood samples were tested at 03 month. We found that PCR test using the Amplicor HIV-1 amplification kit (Roche) to be sensitive in detecting HIV infection in sex workers but the test appeared not sensitive enough to detect HIV-1 infection during the "window" period. We were unable to detect any sex workers with PCR detectable HIV-1 before they seroconverted to become HIV antibody positive. The reason for the failure was attributed to the low infection rate among sex workers and possible lack of sensitivity of the Amplicor PCR/HIV-1 amplification kit to detect early HIV-1 infection. We are currently studying other PCR procedures to improve the sensitivity of the PCR test for HIV-1.