Ninety-six Przewalski's horses (Equus przewalskii) were blood typed using systems of inherited blood variants known to be highly effective for parentage testing of domestic horses (E. caballus). Sixteen red cell antigenic factors detected using sera prepared by alloimmunization of domestic horses were shown to be inherited in six systems (A, C, D, P, Q, and U) and in the same patterns as domestic horses. Family data confirmed autosomal, codominant inheritance at five loci of serum protein variants (Al, Tf, Xk, Pi, and Es) and three loci of red cell proteins (PGM, PHI, and Hb). One serum protein locus (Gc) and two red cell protein loci (PGD and CA) appeared to be monomorphic. Despite the narrow genetic base and high inbreeding coefficients of captive Przewalski's horses, average heterozygosity calculated over 18 loci was estimated to be 0.320 +/- 0.05, which was similar to that found in five breeds of domestic horses.