Four of 12 unlinked polymorphic marker systems were identified as predictors of normal serum cholesterol levels. Consistent effects between males and females and with other studies suggest that these marker loci are themselves involved in cholesterol determination or are closely linked to the involved loci. Two-locus combinations suggest that an 8-9 mg/100 ml difference in nonfasting serum cholesterol may be predicted between phenotypic classes which are not rare in frequency.