Glutamic oxaloacetic transaminase isozymes were purified simultaneously to homogeneity from rat liver with high yields. Three subforms of mitochondrial isozyme and three subforms of cytosolic isozyme were separated by chromatography on CM-Sephadex and electrophoresis on polyacrylamide gel. The general enzymatic properties of the purified isozymes such as their kinetic parameters, isoelectric points, molecular weights, amino acid compositions, NH2-terminal amino acid sequences and COOH-terminal amino acids were determined. Most of these properties of the isozymes are similar to those of the corresponding isozymes from other sources, such as rat brain and pig and human heart. In amino acid compositions, cytosolic isozyme from rat liver has more proline and glycine and less arginine, threonine and leucine than pig heart cytosolic isozyme; the mitochondrial isozyme has more glutamic acid and glycine and less serine than the corresponding pig heart isozyme. The NH2-terminal amino acid sequences of GOT isozymes from rat liver were identical with those of the GOT isozymes from pig heart up to the 10th residues except for the 5th residues. The subforms of mitochondrial isozyme from rat liver were generated on storage at 4 degrees C for 4-8 weeks.