The mechanism of cell death induced by feline immunodeficiency virus (FIV) infection was investigated in an interleukin 2(IL-2)-dependent T-lymphoblastoid cell line (MYA-1). DNA extracted from FIV-infected MYA-1 cells showed a ladder of nucleosomal DNA, indicating that the cytopathic effect (CPE) observed in these cells was due to apoptosis. Infection of MYA-1 cells with FIV was associated with suppression of the proliferative response of the cells to exogenous IL-2 prior to DNA fragmentation. These findings suggest that FIV-induced CPE in these T-lymphoblastoid cells is associated with apoptosis possibly due to a defect in the IL-2 signal transduction pathway.