The genetic and cultural heritability of serum cholesterol and triglyceride concentrations, as well as of the concentrations of low and high density lipoprotein cholesterol and serum apolipoproteins A-I, A-II and B, were estimated by path analysis in families selected through probands with premature myocardial infarction and in families randomly selected from the general population. Genetic heritability was high for serum cholesterol (0.64) and low density lipoprotein cholesterol (0.67) concentrations, whereas it was lower for high density lipoprotein cholesterol level (0.42). Cultural inheritance was of less importance than genetic inheritance for all cholesterol variables. For serum triglyceride concentration genetic (0.33) and cultural (0.23) heritability was of similar significance. The results for serum apolipoproteins A-I and A-II parallelled those for HDL cholesterol. A marked intergenerational difference was found in the genetic heritability for apolipoprotein B concentration. The parental genetic heritability was 0.14, whereas the genetic heritability was 0.51 among siblings.