To investigate the role of genital shedding of herpesviruses in human immunodeficiency virus type 1 (HIV) transmission, we compared 20 HIV-infected men who did and 26 who did not transmit HIV to their sex partners. As described previously, HIV transmission was associated with the potential source partner having higher levels of HIV RNA in blood and semen, having lower CD4(+) T cell counts, having bacterial coinfections in the genital tract, and not using antiretroviral therapy. This study extended these findings by observing significant associations between HIV transmission and the following characteristics, especially among therapy-naive potential source partners: seminal cytomegalovirus (CMV) shedding, seminal Epstein-Barr virus shedding, and levels of anti CMV immunoglobulin in blood plasma.