The proteins of the ruminant erythrocyte membranes were analysed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, and their relations to the slow erythrocyte sedimentation rate (ESR) of the ruminants were investigated by treating the erythrocytes with proteinases such as trypsin, chymotrypsin and pronase, and glycosidases such as neuraminidase and galactosidase. Protein content in the erythrocyte membrane was 2.85 +- 0.28 in human, 3.60 +-0.41 in Korean cattle, 3.71 +- 0.36 in Holstein, 4.13 +-0.83 in Korean native goat and 3.94 +- 0.56 mg/ml in sheep, showing higher in ruminant animals than in human (p0.01). Although the general protein profiles of the ruminant erythrocyte membranes were almost similar to that of human, all the ruminant erythrocyte membranes showed one additional protein band, called band- Q in the previous report on proteins of bovine erythrocyte membrane, which migrated electrophoretically to the mid position between band-2 and band-3 in human erythrocyte membranes. The glycoprotein profiles of ruminant erythrocyte membranes revealed by periodic acid Schiff (PAS) stain showed a marked difference from that of human. The PAS-l (glycophorin) and PAS-2 (sialoglycoprotein) present in human erythrocyte membranes were almost absent from the ruminant animals. Instead, a strong PAS-positive band near the origin of the electrophorograms, which was named as PAS-B in the previous report on proteins of bovine erythrocyte membranes, was shown in the ruminant animals except sheep. In addition, the erythrocyte membranes of Korean native goat and sheep showed a moderate PAS-negative band near the tracking dye of the electrophorograms, which was named as PAS-G in this study. In the erythrocyte treated with the enzymes, the migration of each protein fracture of erythrocyte membranes in response to each enzyme was diverse according to different species or breed of ruminant animals. Among others, band-Q present in ruminants was slightly or moderately decreased by trypsin-, chymotrypsin-, and pronase- treatments of the erythrocytes, but not only in sheep