Antibodies to human T-cell lymphotropic virus type III (HTLV-III Ab) were present in twenty-one out of sixty-four asymptomatic promiscuous homosexual men from Copenhagen. The presence of HTLV-III Ab was associated with lymphadenopathy (P less than 0.0005), cytomegalovirus isolation (P less than 0.01), low skin test reactivity (P less than 0.01) and episodes of fever within the 2 month period prior to investigation (P less than 0.05). No significant differences occurred in the total number of T-cells, T-suppressor cytotoxic cells, T-helper cells or helper to suppressor ratio (H/S ratio) between HTLV-III Ab positive and negative homosexuals. An H/S ratio less than or equal to 1.0 was significantly more frequent in homosexual men who both had HTLV-III Ab and excreted cytomegalovirus (P less than 0.01). The H/S ratio of HTLV-III negative homosexuals were significantly lower than that of the controls suggesting that a non-HTLV-III related immunosuppression occurs among homosexuals. Within 2 years after the investigation AIDS or the AIDS related complex developed in three of the men, who at the first investigation all had HTLV-III Ab, alterations in T-lymphocyte subsets and cutaneous anergy. It is suggested that a combination of T-cell subset determination and determination of HTLV-III Ab may provide more valuable prognostic information than isolated determination of HTLV-III Ab.