The present study was undertaken to evaluate the utility of a gram stain of endocervical secretions in the prediction of endocervical infection with Chlamydia trachomatis. Endocervical examinations, Gram stains and chlamydial cultures were performed on 214 women who were attending a sexually transmitted diseases clinic and were at increased risk for chlamydial infection. Almost 24% of the Gram stains were judged inadequate because of the presence of ectocervical material. However, significantly higher isolation rates for C. trachomatis were found for those women with valid smears and 10 or more polymorphonuclear cells on their smear (44% vs 19%, P = .0008). This relationship was independent of the presence of gonococcal infection. Based on the results of this study, endocervical Gram stains appear to be a valuable screening tool for chlamydial infection, particularly among those without mucopurulent discharge.