The present study was undertaken to evaluate the influence of Ukrain on the free amino acids pool in blood plasma in ten patients with breast cancer, treated in the preoperative phase with the drug. The control group consisted of five patients of similar age and advancement of the disease, who did not receive Ukrain before mastectomy. The data obtained from these studies indicate that Ukrain positively influences the metabolism of amino acids and their derivatives. The most characteristic changes were increase of proline, taurine and glutamic acid.