Polymorphism of human C′3 has been defined by prolonged agarose electrophoresis of fresh serum. At least four, and probably five, alleles have been identified by the electrophoretic mobilities of gene products. Inheritance of three alleles, F1 F, and S, is consistent with the autosomal condominant type. The inheritance of S1 is probably codominant and that of F0·8 is not known. Of the 15 phenotypes predicted by these alleles, eight have been observed.
