Summary: Thirty antigens have been detected in the erythrocytes of cattle, by means of iso-immune sera produced by transfusing blood from one individual into another, or by immunizations of rabbits with bovine cells, or by both methods. Each cellular character appears to be produced by a single gene, although some may be products of linked genes. Since these antigens are passed only directly from parent to offspring, these characters may be used for exclusion in cases of disputed parentage in cattle.