From January through June 1983, 178 male patients with urethritis were investigated on the etiology and epidemiological and clinical features. By using Chlamydia trachomatis direct specimen test (Micro Trak), C. trachomatis was detected in 60 (47.2%) among 127 patients with non-gonococcal urethritis, while it was detected 8 (15.7%) among 51 patients with gonococcal urethritis. The source of infection was a non-prostitute in 30% of chlamydial urethritis, while in gonorrheal urethritis only one patient was infected from a non-prostitute. Mean incubation period of chlamydial and gonorrheal urethritis was 28.5 and 9.2 days, respectively. In chlamydial urethritis, 33.3% of patients did not complain of urination pain and 20.4% showed no urethral discharge. Symptoms of chlamydial urethritis were milder than those of gonorrheal urethritis.