An immunologic and virologic work-up was undertaken in 425 symptom-free multitransfused patients with hemophilias or hemoglobinopathies living in France. Patients were entered into five groups according to the type of blood product they received: local factor VIII, a mixture of local and imported factor VIII, imported factor IX, local factor IX, washed red blood cells. The overall prevalence of IgG antibodies to the lymphadenopathy-associated virus (LAV) was 45%. The highest rate was observed in hemophiliacs who received factor VIII concentrates prepared from plasma collected mainly on the American continent; intermediary values were found for hemophilic patients treated with local factor VIII or factor IX concentrates; and the lowest values were found for those who were treated with washed red blood cells. Lymphadenopathy, decreased skin hypersensitivity reactions, relative lymphopenia, and altered ratio of T lymphocyte subsets occurred at significantly higher rates in patients positive for LAV antibody, although such abnormalities were also encountered in LAV serologically negative patients. A correlation between treatment intensity and immunologic disturbances was found in patients infused with factor VIII preparations, irrespective of their positive or negative LAV antibody status. This study has shown the prominent role of LAV in the occurrence of immunologic disturbances in multitransfused patients. However, allogenic or altered proteins present in factor VIII but not in factor IX concentrates seem to play a role of immunocompromising agents. The interplay between LAV and additional factors possibly leading to acquired immunodeficiency syndrome remains to be analyzed.