The incidence of Chlamydia trachomatis, Ureaplasma urealyticum, Mycoplasma hominis, Neisseria gonorrhoeae and Trichomonas vaginalis was studied in men with urethritis. Out of 150 examined men 48.7% had the positive isolation of U. urealyticum, 26.0% C. trachomatis, 22.7% N. gonorrhoeae, 18.7% M. hominis and in one (0.7%) patient T. vaginalis was found. None of the above mentioned microorganisms was detected in 24.7% of examined men. In 43.3% cases only one agent was isolated. In 23.3% of the men the combination of two agents, in 8.0% the combination of three and in 0.7% even the combination of four studied microorganisms was observed. C. trachomatis was most frequently observed in combination with N. gonorrhoeae (15 cases) and U. urealyticum (14 cases). M. hominis and U. urealyticum occurred simultaneously in 22 examined men.N.gonorrhoeae was most frequently found together with U. urealyticum (16 cases). Concerning the occurrence of other bacteria and yeasts, no significant difference was found between the groups positive and negative for the above mentioned microorganisms.