A group of 63 patients infected by HIV and presenting with CD8 hyperlymphocytosis (CD8+) has been studied. CD8 hyperlymphocytosis was defined by the presence, during at least three months, of at least 1,500 CD8 circulating lymphocytes. The CD8+ patients (n = 63) were identified and followed within the cohort (1,444 patients) of the "Groupe d'Epidémiologie Clinique du SIDA en Aquitaine " (GECSA). CD8+ patients were compared with a control group of 126 HIV infected patients without CD8 hyperlymphocytosis recruited within the GECSA cohort and followed in the same manner during two years. The occurrence of opportunistic infections was less frequent in CD8+ patients. The proportion of patients with a CD4 lymphocyte count below 200/mm3 was lower in the CD8+ group than in the CD8- group at inclusion and at the last check-up (P less than 0.01). A tendency for longer survival and delayed onset of AIDS was noted in CD8+ patients. Such a difference in prognosis might be due to a peculiar cytotoxic response against HIV among CD8+ patients. Further follow-up of a larger group of patients is needed to confirm this hypothesis.