PIP: In recent years, Chlamydia trachomatis infections have been found to be among the major causes of salpingitis throughout the world. In order to determine in the 1st trimester of pregnancy the prevalence of this infection in a previously unscreened population by direct immunofluorescence (Microtrak), we examined 3 groups: women (n=58), infertile women (n=87) and males with subacute urethritis (n=24). Infertility was defined as incapacity to achieve a pregnancy after 12 months of unprotected coitus; subacute urethritis patients had been treated previously for an acute disease and later presented with persistent urethral complaints. The overall prevalence of Chlamydia in all 3 population groups was 13.0% among 169 patients. This rate was divided as follows: pregnant women--8.6%; infertile women--11.5%; men with subacute urethritis--29.2%. Compared to the pregnant group, the infertile and subacute urethritis groups had a significantly high risk of harboring a chlamydial infection. In all female patients, the risk of chlamydial infection decreased with increasing parity, suggesting an association between chlamydial infection and infertility. (author's)