OBJECTIVE To evaluate 1) whether microscopic detection of leukorrhea or bacterial vaginosis identifies patients at high risk for cervical infection with Chlamydia trachomatis or Neisseria gonorrhoeae, and 2) if pregnancy alters the predictive value of these findings. METHODS Wet-mount screening examination of vaginal discharge was performed on all new patients seen at two resident-staffed clinics serving primarily indigent women. Leukorrhea was defined as >10 white blood cells per high-power field on microscopic examination; Amsel criteria were used to determine the presence of bacterial vaginosis, with a positive clue cell test result defined as >20% of epithelial cells. The diagnoses of C trachomatis and N gonorrhoeae infection were established by deoxyribonucleic acid amplification tests. RESULTS The study population consisted of 194 women, 118 (61%) of whom were pregnant. Overall, 11% of women had positive cultures for chlamydia or gonorrhea. Although both leukorrhea and clue cells were independently associated with positive cervical cultures, multivariate analysis found that clue cells did not contribute to the predictive value of leukorrhea alone among both pregnant (relative risk [RR] = 15.7) and nonpregnant (RR = 58.7) women. Negative predictive values for the screening test were comparably high (98-100%), independent of pregnancy status. CONCLUSION Leukorrhea, in the presence or absence of bacterial vaginosis, was strongly associated with cervical infections with C trachomatis or N gonorrhoeae among both pregnant and nonpregnant patients. In settings where patient follow-up is uncertain, on-site screening tests identify women for whom empiric antibiotic therapy for sexually transmitted diseases may be appropriate.