The time course of viral gene expression in H9 cells acutely infected with HIV-1 was analysed by the polymerase chain reaction (PCR). Virus-specific sequences were first detected in genomic DNA of H9 cells 1-2 h after infection. RNA for the regulatory genes such as the tat and nef appeared 2-3 h post-infection and RNA for the gag and env at 3 h. The results demonstrate that viral DNA synthesis occurs rapidly after infection of target cells followed by synthesis of viral RNA. Cell-associated reverse transcriptase activity increased after 24 h, while culture supernatant enzyme activity increased later, between 1-5 days. The delay in virus release after rapid integration and transcriptional activity suggests the involvement of additional factors, perhaps both cellular and viral, that control the formation and budding of mature virions.