Apoptosis is one of the mechanisms involved in the persistent CD4(+) T cell lymphopenia occurring in human immunodeficiency virus (HIV)-infected patients treated with highly active antiretroviral therapy (HAART). The aim of this study was to look at the relationship between the level of T cell apoptosis in patients on HAART and their HIV viral load measurement. Forty-five patients receiving HAART for a median time of 5 months were included: 13 had an undetectable viral load and 32 had a viral load > or = 200 copies/mL. No relationship was observed between the level of spontaneous T cell apoptosis and the viral load measurement. Patients with a viral load > or = 200 copies/mL exhibited a significantly higher level of CD4-induced apoptosis of CD4(+) T cells, compared with patients with undetectable viraemia (38 versus 15%, respectively, P = 0.03). Activation-induced apoptosis may be involved in the paucity of the immune reconstitution observed in HIV-infected patients treated with HAART.