Urethral specimens from 480 heterosexual patients were examined for Chlamydia trachomatis. Chlamydia were isolated from 32.7% of men with non-specific urethritis (NSU), from 16.1% of men with gonorrhoea, and from 4.1% of men without urethritis. Chlamydial isolation was not related to duration of symptoms, presence of discharge, or past history of attendance at the clinic. Urine from 176 heterosexual patients was examined for Ureaplasma urealyticum. Ureaplasmas were present in 53.8% of men with NSU, in 28% of men with gonorrhoea, and in 32.9% of men with no urethritis. Detection rates for ureaplasmas in patients with chlamydia-negative and chlamydia-positive NSU were similar, but ureaplasmas were present in significantly greater numbers in patients with chlamydia-negative NSU than in those with chlamydia-positive NSU.