An inverse association between socioeconomic status, as measured by years of education, and blood pressure has been reported in a number of studies. However, two secular trends may have changed the nature of this relation: a higher mean level of education in the population and intervention for high blood pressure in the community. Given that education is the most commonly used indicator of social class and measurement is a critical issue in epidemiologic research, a study was initiated to examine the validity of education for predicting blood pressure among 11,554 examined persons aged 25-74 years from the Second National Health and Nutrition Examination Survey (1976-1980) or the Hispanic Health and Nutrition Examination Survey (1982-1984). In univariate analysis, a consistent, inverse association between education and blood pressure was found for whites and blacks, but not for Mexican Americans. After adjustment for age and body mass, the effect persisted only for systolic blood pressure in whites. The association of education and blood pressure was positive in Mexican-American females. Education was inversely related to hypertensive status in whites and in black females. These findings suggest that information on education may be of little value for identifying populations at risk of high blood pressure, particularly if age and body mass are known. However, information on education may be of considerable value in the design and implementation of appropriate interventions.