By cultural investigations in 333 males with non-gonorrhoical urethritis (NGU) and 158 control probands it was demonstrated that Chlamydia trachomatis is the main germ of this disease also in the GDR with a frequency of 40% of the cases. A chlamydia-negative NGU was caused in 15% by Ureaplasma urealyticum in a number of greater than or equal to 10(4) germs/ml urine and in 5% by Trichomonas vaginalis, respectively. Candida albicans occurred significant more frequently in the patient group (21%) than in the control group (4%). Other optional pathogenic bacterias were the cause of NGU in single cases. The diagnosis and therapy of NGU should be considered this germ spectrum and the sexual partner also.