Urethral, rectal, and pharyngeal material from 150 men who had had exclusively homosexual contact and who consecutively attended a sexually transmitted diseases clinic was cultured for Chlamydia trachomatis. The organism was isolated from at least one site in 15 (105) patients. The isolation rates from the urethra, rectum, and pharynx were 6 . 7%, 4%, and 1 . 3% respectively.