Zymograms of the aspartate aminotransferase (AAT, EC 184.108.40.206) activity in leaf extracts from Aegilops and Triticum species revealed three AAT zones, denoted according to the decreasing electrophoretic mobility towards the anode as AAT-1, AAT-2 and AAT-3. The AAT activity zymograms of subcellular fractions isolated from T. aestivum seedlings made it possible to establish that the AAT-1 zone is located in the mitochondria, AAT-2 in the chloroplasts and AAT-3 in the cytoplasm. Most of the total AAT activity from wheat leaves arises from the chloroplasts and cytoplasm. The AAT-3 zone exhibited the lowest electrophoretic mobility, but 3 isoenzymes occurring within were the most visibly separated. The occurrence of a single band in this zone at the AAT-3a position (closest to the anode) for the aneuploid CS3ASDt AABBDD line (the absence of long arms of the 3rd pair of homologous chromosomes in the A genome) and at the AAT-3c position for Ae. umbellulata (genome UU), as well as three bands in the whole zone for T. durum (AABB) and T. aestivum (AABBDD) each, made it possible to evaluate the subunit composition of isoenzymes in the AAT-3 zone. The band at the AAT-3a position in the zymogram is formed from dimers, AAT-3b from and AAT-3c from . By comparing the distribution of isoenzyme bands intensities (the result of enzymatic activity) with the mathematical models, the frequencies of the occurrence of the and subunits within AAT-3 zone were evaluated. In AAT-3 from T. durum, and occurred at the ratio of 0.54 : 0.46, and in that from T. aestivum ? 0.62 : 0.38, respectively.