Two patients with hemophilia A had generalized lymphadenopathy, lymphopenia, elevated IgG values, depressed T4 (helper) lymphocytes, elevated T8 (suppressor) lymphocytes, and abnormally low T4/T8 ratios. One of the patients, who also had hepatosplenomegaly, underwent cervical lymph node biopsy; the node contained 43% T8-lymphocytes, a marked elevation over the small fraction of T8 cells usually found in lymph nodes. These patients may have a form of the acquired immune deficiency syndrome described in male homosexuals, Haitians, intravenous drug abusers, and recently, in patients with hemophilia. We studied T cell phenotypes in 43 patients with hemophilia. Fourteen of 28 patients given commercial factor VIII concentrates had abnormal T4/T8 ratios; none of nine patients who used cryoprecipitate had abnormal values. T4 helper cells were significantly lower, T8 suppressor cells significantly elevated, and T4/T8 ratios significantly lower in the lyophilized concentrate users and in patients with hemophilia as a total group. The type of therapeutic factor VIII replacement may alter the risk of developing T4/T8 abnormalities or AIDS.