Jurkat cells stably expressing high levels of the HIV-1 Tat protein were generated after transfection with an Epstein-Barr virus-based episomal replicon and selection in hygromycin B. The Jurkat Tat transfectants exhibited a longer doubling time when compared to Jurkat cells or Jurkat cells transfected with the control parent plasmid. Cell cycle analysis revealed comparable durations of each phase of the cell cycle in the Tat and control transfectants. Flow cytometric analysis using Hoechst 33342 and propidium iodide staining revealed that the Tat transfectants exhibited a higher percentage of apoptotic cells when compared to the control transfectants (29.1 ± 3.1 vs. 11.43 ± 3.1%). Incubation of Jurkat cells with recombinant HIV-1 Tat protein resulted in induction of apoptosis. The HIV-1 Tat protein induces apoptosis in a CD4-positive T cell line. Tatinduced programmed cell death may contribute to the lymphocyte depletion seen in persons infected with HIV-1.