In the last years the number of HIV-positive patients needing cardiac surgery has greatly increased. Cardiopulmonary bypass is suspected to have a role in the progression of HIV-infection to acquired immunodeficiency syndrome (AIDS). From October 1988 to December 1990, 6 intravenous drug addicts underwent cardiac surgery for infective endocarditis at our Department. Preoperative and postoperative absolute lymphocyte T-helper (CD4) and T-suppressor (CD8) counts did not show a close association between the temporary lymphopenia induced by cardiopulmonary bypass and progression to AIDS.