Cytosolic and mitochondrial isozymes of aspartate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase [EC 2. 6. 1. 1]) were purified to homogeneity from rabbit liver. The rabbit liver isozymes were closely similar to the corresponding isozymes from other sources, including human heart, pig heart, chicken heart, and rat liver, in their molecular weights, absorption spectra, amino acid compositions, isoelectric points, and Michaelis constants for the substrates. The NH₂-terminal amino acid sequences of rabbit liver isozymes were identified up to 30 residues, and showed some differences from those of the corresponding isozymes obtained from other animals so far studied.