A group of 180 men who visited Urology Department of Severance hospital, including 115 patients with nongonococcal urethritis (N.G.U.), 27 patients with prostatitis, 13 patients with gonococcal urethritis (G.U.) and 25 healthy medical student controls were investigated for the isolation of Ureaplasma urealyticum (T-strain mycoplasma) from the specimen of ureaplasma discharge, urine and semen. Taylor-Robinson media of T-broth and T-agar was used for the isolation of Ureaplasma urealyticum. To the best of our knowledge, the study on the culture of Ureaplasma urealy ticum was reported for the first time in Korea. The followis g results were obtained: 1. The isolation rate of Ureaplasma urealyticum in nongonococcal urethritis (53.0%) revealed highest of those in the other three groups of prostatitis, gonococcal urethritis and control (40.7%,38.4% and 16.0% respectively). 2. As for the specimens, urethral discharge revelaed higher isolation rate of Ureaplasma urealyticum (54.6%) than first voided urine (50.0%). 3. The more consorts patients had, the higher positive culture rate of Ureaplasma urealyticum were revealed. The isolation rate in case of more than one causal in nongonococcal urethritis (27.8%) revealed much higher than in case of marital only (5.2%), one regular (6.1%) and one causal 03.9%). 4. 2.6% of isolation rate of Ureaplasma urealyticum revealed in patients with nongonococcal urethritis who visited the clinic in later than 4 weeks after the symptoms developed. However, the isolation rate in patients who visited within 4 weeks revealed 50.3%. The lower isolation rate of Ureaplasma in the late treatment seekers might be probably due to the suppression effect against Ureaplama urealyticum from the possible previous self antibiotic treatment. 5. Attachment of Ureaplasma urealyticum mostly to the neck and head portion of the spermatozoa seemed to playa role to affect the motility of sperms.