Fifty-five women with suspected pelvic inflammatory disease underwent diagnostic laparoscopy and endometrial and tubal biopsy, with specimens for isolation of Chlamydia trachomatis and for staining with a species-specific monoclonal fluorescein-conjugated antibody to C. trachomatis were obtained from the urethra, rectum, endocervix, endometrium, tubes, and cul-de-sac. C. trachomatis was isolated from 21 patients (38%), including 10 (18%) who had positive endometrial or tubal cultures. The fluorescein-conjugated antibody stain was positive for 43 (86%) of 50 culture-positive specimens, for 14 (18%) of 78 culture-negative specimens from 21 patients who had positive cultures from other sites, and for one (0.5%) of 192 specimens from 34 patients who had negative cultures at all sites. Thus the sensitivity of direct fluorescein-conjugated antibody for culture-positive specimens was 86% and the specificity for specimens from culture-negative patients was 99%. Twelve upper genital tract specimens were positive by fluorescein-conjugated antibody only. Fluorescein-conjugated antibody staining of 50 paraffin-embedded endometrial aspirates showed extracellular or intracellular elementary bodies and or cytoplasmic inclusions in all of seven culture-positive specimens, in four of six culture-negative specimens from patients who had positive cultures at other sites, and in none of 34 specimens from patients with negative cultures. Thus fluorescein-conjugated antibody staining is useful for confirming the role of C. trachomatis in endometritis and salpingitis. It is more sensitive than culture for detection of chlamydia in endometrial or tubal specimens and is able to confirm that the organism is actually present in endometrial tissue (rather than simply reflecting contamination from the cervix) in women with clinical evidence of pelvic inflammatory disease.