A genetic epidemiological study of serum lipid and lipoprotein levels was conducted among families of Marwaris residents in Calcutta. A total of 210 families, comprising over 100 individuals, were studied. Analyses were performed to estimate the genetic and environmental effects on the determination of high density lipoprotein cholesterol (HDL-C) and serum triglycerides (TG). Familial correlations for HDL-C and TG were estimated: parent-child and sib-sib correlations were found to be significant. Spouse correlations were not significant. Correlations between environments of siblings were significant. Genetic analysis of data on HDL-C and TG performed under a path model, taking genetic transmission and possible environmental associations among family members into account, indicated that lipid and lipoprotein levels adjusted and standardized for age, gender, education, occupation and disease status are primarily determined by genetic factors. The effects of environmental factors were also significant, although in comparison with genetic factors these effects were much smaller. The estimated genetic heritability for HDL-C was approximately 80 per cent, while that for TG was approximately 55 per cent. The genetic effects and environmental effects were not significantly different between adults and children.