In our early experimental (with W-256, SM-1 and PC-1 tumors) and clinical (breast, bladder and prostate cancers) studies the use of the anticancer drug NSC-631570 was proven to be safe and highly effective, inhibiting protein synthesis in cancer cells, selectively accumulating in cancer tissue after a single intravenous administration and controlling cancer-induced metabolic imbalance. This drug inhibits metabolic processes in the tumor and causes metabolic disorders in cancer cells. Moreover, NSC-631570 induced the changes in certain amino acids concentrations in biological fluids and tumor tissue in animal models and cancer patients. These changes cannot be explained by metabolic amino acid disorders in cancer known so far. In this study the effects of NSC-631570 on blood plasma amino acids has been investigated. Blood was sampled from 10 healthy donors and 29 patients with different types of cancer (stomach, rectal, lung, breast, bladder, prostate, and leukemia). Comparison of NSC-531570 effects in plasma of healthy donors and cancer patients has shown, that this compoumd: 1) affects amino acids with positively charged (His, Arg) or not charged (Tyr, Thr, Gln) R-groups; 2) decreases concentration of His and increase the concentrations of beta-Ala and Tau. These changes depend on the concentration of NSC-631570 and the type of cancer. On the basis of the literature data and the results of our studies we suggest that Ukrain's biological actions in cancer are realized at least partly through selective interaction with amino acids, their derivatives, and plasma proteins. These data provide the background for the using Ukrain in the cancer detection and investigating the mechanisms of carcinogenesis.