We studied two population groups (more than 1,600 patients) to determine the prevalence and clinical associations of genital tract infections with chlamydiae and herpesviruses. Base-line isolation rates for asymptomatic women having routine pelvic examinations were much lower than rates for symptomatic women. In both groups, chlamydiae were more prevalent than herpesviruses. Chlamydial infection was associated much more commonly with cervicitis (36.6%) than with vaginitis only (4.1%). Among 282 symptomatic men, the cultures of 19.9% yielded chlamydiae, and 4.3%, herpesviruses. Chlamydiae were recovered from 35.5% (27 of 76) of specimens from men with nongonococcal urethritis, and from an even larger proportion, 57% (24 of 42), of the specimens from men with frank discharge.