The present study was designed to determine whether there was a significant correlation between the clinical presentation of patients with AIDS or AIDS-related illnesses and the degree of their underlying immunologic abnormalities. In 17 patients who presented with opportunistic infections, the mean number of T4 lymphocytes was 34/mm3 and the mean proliferative response to phytohemagglutinin 26,000 cpm; in 12 patients who presented with Kaposi's sarcoma alone, the mean number of T4 cells was 231/mm3 and the mean proliferative response to phytohemagglutinin, 32,809 cpm; and in nine patients with the lymphadenopathy syndrome, the mean number of T4 cells was 703/mm3 and the mean proliferative response to phytohemagglutinin, 49,317 cpm. These findings suggest that those patients who present with opportunistic infections as their initial clinical manifestation of AIDS may represent a subgroup with a more severe immunologic derangement prior to clinical diagnosis. Thus, in those who have a predisposition to Kaposi's sarcoma, this disease will often develop, prior to the development of T cell dysfunction, to the degree of that in those who present with opportunistic infections. This finding is of importance in attempts to understand the pathogenesis of this syndrome and in the design of therapeutic trials.