Аннотация:The combined effect of semax with aqueous solutions of lead diacetate (10-7 M) and ammonium molybdate (10-5 M) on the formation of a conditional two-way avoidance reaction in rats in a shuttle chamber was studied. It was found that both heavy metal salts inhibit learning and memory; lead diacetate caused greater depression. Semax slowed down the production of the conditional reaction, but counteracted the neg- ative influence of both metals on this process. At the same time, the influence of semax on the formation of the avoidance reaction in the presence of ammonium molybdate, which in itself inhibited avoidance, paradoxically intensified. With the combined effect of the peptide and ammonium molybdate, the formation of a conditional reaction occurred much faster than against the background of semax without combination with molybdenum. In general, the data obtained indicate that semax counteracts the neurotoxic effect of lead and molybdenum salts. Since the main mechanism of the neurotoxic effect of heavy metals is oxidative stress, the indicated pos- itive effect of semax can, in our opinion, serve as confirmation of the presence of antioxidant properties in the spectrum of pharmacological activity of the peptide. https://doi.org/JCPP.2023-2-2.12-15