Further studies are needed to define the clinicopathologic manifestations of CT infection. Many questions remain regarding the natural history and pathogenetic mechanisms of CT and its biologic and clinical interactions with other prevalent STDs. However, it is apparent that CT is a major cause of STD in the Western world and that its incidence and prevalence have increased to epidemic proportions in young, sexually active women and men. As with other STDs, epidemiologic control of CT infection is of paramount importance. The clinician and pathologist should develop a heightened awareness of the probability of Chlamydia infection in all patients at risk for STD, and in clinical settings, only a high index of suspicion will result in timely therapeutic intervention. Although more simplified and less expensive diagnostic procedures for CT are being investigated, presently, culture isolation is the best and most accurate diagnostic method for CT genital infection and its use should be popularized and made more easily available. Immunofluorescent staining using monoclonal and heterologous antibodies to extracellular CT elementary bodies in preselected smears appears promising as a diagnostic technique and requires further study. There is no apparent role for the use of routine cyto- and histologic microscopy in the diagnosis of CT infection and the practice of diagnosing presumed chlamydial vacuoles or inclusions from cervicovaginal Pap smears should be actively discouraged. Although CT cervicitis plays a dominant role in the pathogenesis and dissemination of CT infections, it should be remembered that multiple sites of genital involvement occur commonly with CT infection and this multifocality should be considered when CT cervical cultures are negative and in post-treatment follow-up. Cultures should be obtained from sites of suspected involvement and should include scrapings or biopsy sampling of the tissue surface to insure the presence of sufficient numbers of epithelial cells. Local secretions or exudate should not be considered adequate. In the female, sampling of the urethra, rectum, and endometrium may facilitate accurate diagnosis. Scraping or sampling of the tubal epithelium by biopsy may provide diagnostic material in acute salpingitis and PID and should be considered if laparoscopy or laparotomy are performed. Routine screening by culture for CT cervicitis has been suggested in high-risk clinical groups and in antepartum patients for prophylaxis of fetal and neonatal disease and requires serious consideration because of the high prevalence of CT infection.(ABSTRACT TRUNCATED AT 400 WORDS)