Thirty-nine homosexual males, 11 of whom suffered from AIDS and 13 from Lymphadenopathy Syndrome (LAS), 18 healthy hemophiliacs and 12 healthy blood donors, not belonging to any AIDS risk group, were tested for IgG antibodies to Human T-lymphotropic retrovirus type III (HTLV-III) by indirect immunofluorescence. All tested people were from the area of Amsterdam or from elsewhere in The Netherlands. Five of 11 AIDS patients, 8 of 13 LAS patients and 5 of 15 healthy homosexuals had antibodies to HTLV-III. Five of 18 healthy hemophiliacs were seropositive for HTLV-III. None of the 12 blood donors was seropositive for HTLV-III.