HTLV III and LAV, retroviruses which have recently been described in the United States and France and which seem to be different isolates of the same virus, are closely associated with the acquired immune deficiency syndrome (AIDS) and the lymphadenopathy syndrome (LAS). Sera from male homosexuals from the Federal Republic of Germany with AIDS or LAS were examined for antibodies to HTLV III (anti-HTLV III) by means of the enzyme linked immunoadsorbent assay (ELISA) and by an indirect immunofluorescence assay. 53% of the patients were anti-HTLV III positive as were 20% of symptomless homosexual men.