Cytomegalovirus (CMV) was cultured from the urine of 14 of 190 homosexual but none of 101 heterosexual men attending a venereal disease clinic (P less than 0.005). Viruria was confined to men less than 30 years of age and was present in 14% of this group. Antibody to CMV was measured in the sera of 139 homosexual and 70 heterosexual men attending the same clinic and in 103 male volunteer blood donors. Titers were found in 94% of homosexual patients but in only 54% of heterosexual patients (P less than 0.005) and 43% of male volunteer blood donors (P less than 0.005). The data suggest that sexual transmission is an important mode of spread of CMV among adults and the homosexual men are at greater risk for CMV infections than are heterosexual men. Homosexual men might considered candidates for the evaluation of the efficacy of CMV vaccines in preventing horizontal transmission of infection.