Familial associations of total cholesterol, low density lipoprotein cholesterol, triglycerides, and very low density lipoprotein cholesterol were examined in a population-based random sample of 858 white and 73 black probands and their 4,027 white and 245 black relatives from nine North American Lipid Research Clinics. Correlations among biologic relatives were highly significant for total cholesterol and low density lipoprotein cholesterol and to a lesser extent for triglycerides and very low density lipoprotein cholesterol in whites. Correlations for spouses, however, were not significant, suggesting a stronger influence of genes than shared environment in the determination of these traits. Homogeneity of familial correlations across age strata, clinics, and racial groups was examined. In general, correlations were homogeneous across age strata and clinics, and there was no asymmetry in parent-offspring correlations by the sex of the parent or offspring. Racial differences in correlations were not significant except in four of 32 comparisons, with blacks showing weaker correlations than whites in those instances.