Recently we reported an affinity chromatography method to purify alpha-aminoadipate aminotransferase (AadAT) activity from rat kidney supernatant fraction. Using the same affinity column, we purified AadAT activities from rat kidney and liver mitochondria. The physical and kinetic properties such as pH optima, Km for substrates, molecular weight, subunit structure, isoelectric pH, electrophoretic mobility and inhibition by dicarboxylic acids of mitochondrial AadAT were similar to those of the AadAT from rat kidney supernatant fraction. These results indicate that AadAT from different subcellular fractions is structurally and immunologically identical.