On fruit fly, Drosophila melanogaster there was studied the possibility of antimutagenic correction of factors simulating exogenous xenobiotics, potentially dangerous for humans: lead compounds (II) and the drug ceftriaxonum, and their combinations. Research on the criterion of accounting the dominant lethal mutations (according to P.Ya. Shvarzman) showed (Pb (II) 10-5 M, ceftriaxonum 0,008 g per 100 g the nutrient medium) in studied doses to give rise correspondingly the gain in the frequency of occurring mutations de novo in generative cells by 3.8 and 5.9 times (relatively to the spontaneous level). Co-administration of these substances (at same doses) fails to cause synergistic effects: the frequency of lethal dominants in the experimental group relatively to the level of intact male fruit flies increases by 7.4 times. The aqueous extract of grass Amaranthus retroflexus L. (at a dosage of 0.43 ml per 100 g of the nutrient medium) had pronounced antimutagenic effect. The portion of mutations induced by lead ions was diminished by 54.4%, in the case of ceftriaxonum - by 37.4%, indicating to a specific antioxidant jugulating of free radical mutagenesis. Against the background of the combined effects of both the extent of damaging factors the antimutagenic activity of the complex of biologically active substances from Amaranthus retroflexus L. appeared to be the greatest - 70.7%. Various variants of the experiment simulating the conditions of the prevention or treatment (Amaranthus r. infusion before or after administration of the complex mutagens, respectively) showed a pronounced effect in both cases. In the case of preventive protection of the genome the degree of jugulating of adverse manifested symptoms was 70.7%, and in the case of possible treatment options - 68.8%. In this aspect, it is appropriate the further investigation of biologically active substances from Amaranthus r. L. with the aim to isolate of the spectrum of the most active compounds against exogenous xenobiotics and their introduction in the pharmacological practice.