The role of Chlamydia trachomatis in the cause of male infertility is under discussion. This paper attempts to summarize data from the literature, which support the role of C. trachomatis in male infertility or oppose this suggestion. The following observations are based on a survey of the literature: 1) Chlamydia trachomatis is a frequent pathogen in male genital inflammation, the micro-organisms are rarely present in healthy men. 2) Without doubt, C. trachomatis causes inflammations of the male urethra and the epididymis. Prostatitis and glandulitis vesicalis are discussed controversially. 3) Chlamydia trachomatis antigen or DNA is not demonstrable in secretions of the male accessory glands including the semen with sufficient reproducibility. However, it is easily demonstrable in urethral swabs and the urine. 4) Determination of chlamydial antibodies in serum or semen does not conclusively indicate a current infection with C. trachomatis. 5) There are no conclusive studies showing that men infected with C. trachomatis are less fertile than uninfected men. 6) The male genital chlamydial infection is a threat to the female genital organs, because C. trachomatis infection of the female genital organs may be deleterious to female fertility.