Ureaplasma urealyticum (T-mycoplasma) was isolated more frequently and in heavier growth from cervical mucus (49%) than from vaginal fluid (34%). It was isolated in 24% of vaginal fluid samples and in 35% of cervical mucus samples from fertile women, and in 29% of vaginal fluid samples and in 47% of cervical mucus samples from infertile women. The incidence of infection was high following abortion or total hysterectomy and during pregnancy or oral contraceptive use. T-mycoplasma was also isolated from the vaginal fluid and cervical mucus of a woman with tubo-ovarian abscess, but was not present in women with Trichomonas vaginalis infection. U. urealyticum did not alter the physiophysiologic characteristics of vaginal fluid and cervical mucus or the sperm penetration and sperm viability in cervical mucus. Treatment with tetracycline eradicated the organism in 88% of the infected women. Pregnancies were recorded during a 6-month follow-up in 1 of 19 infertile women who were treated with tetracycline.