Eighty-nine homosexual men participated in a study of sexual practices, T-cell subsets, and antibody titers to cytomegalovirus (CMV) and Epstein-Barr virus (EBV). The prevalence of antibody to CMV was 96% and to EBV, 94%. Titers to CMV were higher in those practicing receptive anal intercourse. The CMV antibody titers were positively correlated with the T-helper/suppressor ratio, number of partners and venereal disease episodes, number of T-suppressor cells, and EBV titers. Twelve percent of the participants had a low ratio only, 18% T-suppressor augmentation, and 3% T-helper deficiency. The CMV titer and prevalence of receptive anal intercourse were higher in those with a low ratio only, T-suppressor augmentation, and T-helper deficiency. These results suggest that CMV infection is acquired through receptive anal intercourse and is associated with an increase in T-suppressor cells and, in some persons, a decrease in T-helper cells.