The general objectives of the CAMAC are: (a) To provide the biostatistical support to better understand the nature history of HIV infection (b) To conduct the appropriate biostatistical analyses to determine the risk factors, and appropriate interventions to limit the spread of the disease and to (c) biostatistically help characterize any biologic or environmental factors which will alter the natural history of the disease (e.g., either limit or accelerate the morbidity and mortality associated with infection) in this population. The specific objectives of the CAMAC study are: (1) To provide the biostatistical support to study the natural history of HIV infection among a population of homosexual men who analyzing the demographic, socio-cultural and behavioral self-report data and by statistically correlating this data with physical examination findings, HIV antibody status, immunologic and blood chemistry and hematology parameters and the presence of antibodies to other viruses. (2) To statistically estimate the rate of disease progression of infection by comparing laboratory findings (HLA-type, CBC, SMA-12), immunologic parameters (by flow cytometry), physical examinations, neuropsychiatric evaluations and electromechanical findings (EEG, EKG, MRI, CAT, nerve conduction studies, radiographic findings) with behavioral events. (3) To statistically estimate the rate of seroconversion among sexually homosexual men as well as determine those behaviors which may alter the rate of seroconversion. (4) To statistically estimate the nature and extent of co-virus infections among sexually active homosexual men.