At two week intervals specimens were taken from 24 prostitutes working in two brothels and cultured for urogenital infection with Chlamydia trachomatis and Neisseria gonorrhoeae. Demographic and clinical data were also collected. C trachomatis was found initially in four and N gonorrhoeae in two of the 20 women at risk of infection. During the study period three new chlamydial and gonococcal infections were diagnosed, resulting from 949 unprotected contacts. Eight women (33%) had developed salpingitis, in contrast to 15% in the general female population. An attempt was made to estimate the infectivity of C trachomatis for the prostitutes. The epidemiological importance of the chlamydial and gonococcal reservoir in the prostitutes was also considered.