Immunoglobulin G antibodies to lymphadenopathy-associated virus have been detected in two groups of French hemophiliacs and in one group of Belgian hemophiliacs, whose mode of treatment differed. Seropositivity was more frequent (58.9%) in patients heavily transfused with blood products of French and foreign origin than in less frequently transfused persons (10.3%). The Belgian group, treated only with local products, showed the lowest frequency of seropositivity (3.4%). In healthy French controls, 1 of 330 had antibody to the virus. The results indicate transmission of lymphadenopathy-associated virus via blood-derived products.