AIDS-related Epstein-Barr virus (EBV)-associated T cell lymphomas are emerging as a new, distinct histopathological entity. The pathway whereby EBV infects T cells as well as the initial EBV transcriptional program in T cells has not been established. In order to shed light on the early events of the EBV infection of T cells, we have used in situ reverse transcription based polymerase chain reaction (RT-PCR) to study the initial EBV transcriptional program in homogeneous CD4+ and CD8+ lymphocytes. Following EBV infection, Epstein-Barr nuclear antigen (EBNA) expression could be detected in T rosetting CD4+ and CD8+ T lymphocytes. Only a few cells showed viral capsid antigen (VCA). EBV immediate-early gene transcripts (BZLF1, BRLF1, and BMLF1) encoded in the BamHI Z, R, and M fragments could be detected by in situ RT-PCR in the EBV producer cell line B95.8. Both BZLF1 and BRLF1 immediate-early transcripts, but not BMLF1 transcript, could be detected in individual CD4+ and CD8+ T cells infected with EBV. Demonstration of EBV mRNA transcripts encoding immediate-early transcriptional transactivators in EBV-infected T cells provides the first evidence for a possible mechanism whereby EBV could contribute to T cell proliferation and EBV-associated T cell malignancies.