Abstract The activity of 11 aminotransferases in homogenates of thyroid glands of normal pigs and human patients with nodular goiter was investigated. Assays were performed using the chromatographic method, with α-ketoglutaric acid as the acceptor of amino groups. In pig thyroid glands, the highest activity is that of aspartate aminotransferase. Less active are alanine, phenylalanine, and branched-chain amino acid (valine, leucine, and isoleucine) aminotransferases. The activity of tyrosine, tryptophan, glycine, and methionine aminotransferases was very low. In homogenates of thyroid glands taken from patients with nodular goiter a high activity of aspartate, valine, leucine, and isoleucine aminotransferases has been observed. The transamination rate of alanine, phenylalanine, and histidine was significantly lower and the transamination rate of other amino acids was negligible. The role of aspartate and aspartate aminotransferase in the thyroid gland was discussed.