A polymerase chain reaction (PCR) was used to demonstrate the presence or absence of Mycoplasma genitalium in the lower genital tract of 57 women who attended a sexually transmitted diseases clinic. The mycoplasma was detected in the cervix of 10 (17.5%) women and also in the vagina of 4 (16%) and the urethra of 6 (24%) of 25 women from whom multiple samples were obtained. Chlamydia trachomatis was detected also by a PCR in 9 (16%) of the women, but only 3 were chlamydia-positive and mycoplasma-positive. M. genitalium was detected occasionally in women with vaginal disease (for example, bacterial vaginosis), whereas C. trachomatis was not, but whether there is any causal relationship between the mycoplasma and vaginal or cervical disease requires further study.