The reactivity of a non-specific reagin (RPR) test and a specific treponemal (FTA-ABS) test were determined in 21 patients with primary syphilis, 430 patients with proven non-treponemal genital ulcerations and 719 patients with acute urethritis presenting at a clinic for sexually transmitted diseases in southern Africa. Excluding those 21 cases of primary syphilis, 358 of 1149 tests performed (31%) were found to be reactive by at least one test. The rate of false positive RPR tests was very low (0.02%). Significantly higher rates of seropositivity were detected in patients with genital ulcerations than in patients with acute urethritis. The highest rates were detected among patients with proven lymphogranuloma venereum (34% RPR positive, FTA-ABS positive; 19% RPR negative, FTA-ABS positive). The geometric mean titres (GMT) of positive RPR tests in non-treponemal infections were found to be lower than in darkfield positive cases of genital ulcer disease.