We used the 1978 National Health and Nutrition Examination Survey to examine the prevalence of positive syphilis serologies in the US population. Analysis of risk markers--gender, age, marital status, education, income, and residence--indicates that all except gender are associated with syphilis seroreactivity, independent of race. Controlling for associated risk markers, the Black-White odds ratio of syphilis seroreactivity is 4.7 (95% CI = 2.7, 8.2). Current knowledge of racial differences in sexual and health care behavior does not explain the Black-White difference in the prevalence of syphilis seroreactivity.