From 1991 to 1996, a cross-sectional study was conducted to test the hypothesis that differences in hypertension prevalence were primarily related to differences in SES. The higher prevalence of hypertension among the high SES Nigerian professionals was thought to be related to higher weight, caloric intake, Westernization of diet, alcohol intake, sodium intake, cardiovascular reactivity, and stress due to job, migration, and change in SES, and to reduced potassium intake and physical activity. Civil servants were systematically sampled from civil service employee lists. Data were collected on blood pressure; urinary sodium, potassium, and protein; diet; anthropometry; electrocardiogram; serum insulin; stress in the work environment, migration history, and cardiovascular reactivity.