High density lipoprotein cholesterol data on a population-based random sample of 858 white and 72 black probands and their 3935 white and 205 black relatives were collected from nine North American clinics using a common protocol and standardized methodology. Familial associations were examined within clinics for whites and pooled across clinics for blacks. The influence of covariates and varying family size on correlations was examined using several sets of transformed and adjusted values and a variety of weighting schemes. Parent-offspring and sibling correlations were significant in most cases, but spouse correlations were not, suggesting a stronger influence of shared genes than shared environment on high density lipoprotein cholesterol. Adjustment for covariates tended to weaken the correlations, but the effect of variable family size was imperceptible. Although pairs involving pediatric offspring or siblings tended to show higher correlation than their adult counterparts, the differences were not significant. All correlations except father-daughter and brother-brother were homogeneous across clinics in whites. There was no asymmetry in parent-child correlations by the sex of the offspring, but the pooled mother-child correlation was significantly higher than father-child values, suggesting a possible maternal influence on high density lipoprotein cholesterol. No heterogeneity in correlations in high density lipoprotein cholesterol was detected between blacks and whites except for mother-son pairs.