Benzidine staining of starch gels after electrophoresis of sera to which haematin was added revealed polymorphism of haemopexin in sheep, mouflon and goat. In sheep three phenotypes were observed, Hpx A, Hpx AB and Hpx B. Pedigree data support the hypothesis of codominant inheritance from a single locus by two alleles, HpxA and HpxB. Neuraminidase treatment of haemopexin preparations showed that Hpx B covered two variants, B1 and B2, thus indicating genetic control by three alleles (HpxA, HpxB1 and HpxB2). In sheep populations the frequency of HpxB is low. In mouflon, in addition to the two variants that are like those of sheep, absence of haemopexin was observed in some animals, by using starch gel electrophoresis as well as immunoelectrophoresis. In goat, three phenotypes were detected, Hpx A, Hpx AB and Hpx B, differing in migration from those of sheep. Haemopexins of the studied species are heterogeneous. Sialic acid is responsible for electrophoretic heterogeneity of sheep haemopexin. Chemical composition (amino acid and carbohydrate), molecular weight (56 060) and N-terminal sequence (Leu-Pro-Pro-) of sheep haemopexin were also determined.