The aim of this study was to determine the frequency of Ureaplasma urealyticum biovars 1 and 2 among 340 men with or without nongonococcal urethritis (NGU) attending a venereal disease clinic in Sweden. NGU was defined by the presence of at least four polymorphonuclear leukocytes per microscopic field (x1,000 magnification) on a smear in which Neisseria gonorrhoeae could not be detected. Ureaplasma urealyticum was detected by polymerase chain reaction, and biovar determination was performed directly on the amplicons by liquid hybridization with biovar-specific probes. Patients with NGU were younger, had had more sexual partners, and exhibited symptoms of urethritis more often than patients without NGU. Ureaplasma urealyticum was detected with the same frequency among patients with and among those without NGU. Among patients with NGU, Ureaplasma urealyticum-positive men were more frequently symptomatic than Ureaplasma urealyticum-negative men. Among patients without NGU, Ureaplasma urealyticum-positive men had had more sexual partners than Ureaplasma urealyticum-negative men. Ureaplasma urealyticum biovar 2 was detected more often among patients with NGU than among those without (P=0.012). Logistic regression analysis was performed using detection of biovar 2 as the response variable and the following four variables as explanatory variables: presence or absence of NGU, symptoms of urethritis, number of partners, and age < or = 24 years. The only association found was that between Ureaplasma urealyticum biovar 2 and age < or = 24 years. More studies should be conducted to determine the possible pathogenic impact of Ureaplasma urealyticum biovar 2.