545 male patients with a tentative diagnosis "urethritis" were examined between November 1984 and December 1994 in the Department of Dermatology and Venerology of the Military Hospital in Ulm. The patients, aged from 18 to 58 years (mean age 24.1 years), were examined according to a standardized diagnostic procedure: Smear preparations from the urethra with subsequent gram staining, bacterial cultures for aerobic bacteria, Neisseria gonorrhoeae (cultures and Phadebact gonococcus test), mycoplasma cultures (Mycoplasma hominis (M. hom.); Ureaplasma urealyticum (U. u), and Chlamydia trachomatis using several methods, primarily DIFT (Syva Micro-Trak). Trichomonas vaginalis counts in urine sediment 441 patients (81%) had 4 or more leukocytes per high-power (x1000) field in the gram stained specimens. In these 441 urethritis-patients the following germs could be detected: Trichomonas vagin 3 (1%), N. gonorrhoeae 80 (18%), Mycoplasma 94 (21%) [U. u. 59, M. hom. 24, both 11], C. trachomatis 114 (26%), other pathogenic bacteria 135 (31%). In 114 patients (26%) no bacteria could be identified. A single infection was diagnosed in a total of 242 patients (55%), a double infection was determined in 71 patients (16%) while a triple infection was found in 14 patients (3%). The spectrum determined in the single infection included the following: N. gonorrhoeae 41 (9%), Mycoplasma 45 (10%), C. trachomatis 67 (15%), other pathogenic bacteria 89 (20%) (most frequently found germs were Enterococcus, beta-hemolytic Streptococcus, Escherichia coli, Staph. aureus). In the double infections combinations with aerobic bacteria dominated. In triple infections, mycoplasma were most common. During the investigation period the number of patients with urethritis symptoms declined at a constant rate.