A total of 240 families were identified from completed community surveys in Maywood, Illinois and Ibadan, Nigeria. Probands were ages 45-55 and equally divided between males and females. A minimum of five first-degree relatives were examined in each family to obtain information on the following variables: blood pressure (BP), obesity, urinary sodium and potassium, socioeconomic status and physical activity. In addition, plasma and DNA were collected and stored for future studies of relevant physiologic intermediate phenotypes and candidate genes for hypertension in the two contrasting populations. These data provided the basis for examining familial aggregation of blood pressure/hypertension and related CV risk factors. Three primary goals were addressed: 1) to determine whether the familial aggregation of blood pressure in Black populations was influenced by the overall distribution of environmental factors at the population level, by contrasting the distribution of familial correlations of blood pressure and the familial aggregation of hypertension, in Nigeria and the United States; to determine the significance of measured environmental correlates of blood pressure by comparing the magnitude of variance components for probands and relatives in each setting; and 3) to use path analysis to obtain estimates of genetic and cultural heritability of blood pressure, controlling for clustering environmental factors at the household level. Plasma and DNA samples collected in this study provided additional valuable resources for future molecular research.