A comparative evaluation of reagin tests (Wassermann, VDRL, RPR) and fluorescent treponema antibody absorption tests (FTA-ABS) performed on blood specimens from 5 271 persons (2 493 pregnant women, 1 130 apparently healthy prospective employees, 1 345 newborn babies and 303 leprosy patients) showed that 17,2% of the pregnant women, 11,95% of the prospective employees, 19,0% of the newborn babies, and 27,2% of the leprosy patients gave positive reactions in one or more of the tests. The majority of specimens were from Cape Coloured patients. FTA-ABS tests allowed the exclusion as biological false positives of ±30% of the pregnant 'positive reactors', of ±37% of the prospective employees, 40,2% of the newborn babies, but only 1% of the leprosy patients. The FTA-ABS test, therefore, deserves wide acceptance as the standard by which the diagnosis of syphilis is confirmed and false positive reactions are defined, although non-specificity in pregnancies, intracellular infections and auto-immune diseases occurs. The classical reagin tests are of value in the control of treatment.S. Afr. Med. J., 48, 1191 (1974).