Experiments were made on rats using step-through passive avoidance method to study the effect of the benzodiazepine medazepam (Mz) on the retention of the memory traces during tests on the 3rd hour, 24th hour and 7th day after training, as well as the influencing of this effect by the nootropic agents meclofenoxate (Mf), aniracetam (Anc) and Euclidan (Eucl.). All substances tested (Mz in a dose of 5 mg/kg weight, Mf - 100 mg/kg, Anc and Eucl - 50 mg/kg), applied both independently and in combination, were administered orally for six days prior to the training. Mz was found to impair the retention of the memory traces in all three tests. Meclofenoxate totally eliminated the memory-impairing effect of Mz. A marked antiamnestic effect of both Anc and Eucl was observed in similar experiments with scopolamine-induced (2 mg/kg i.p.) amnesia. Bearing in mind the results of other behavioural and biochemical studies, including radioligand tests, an attempt is made to justify the idea that the basic mechanism of the amnestic action of Mz is connected with the cerebral cholinergic neurotransmission. The results of the experiments using Opto-Varimex and Automex equipment for testing the effects of Mz, Mf, Anc and Eucl, and of the combination of Mz with the nootropic agents studied, on the spontaneous motor activity of the experimental rats, lead to the most general conclusion that Mz impedes the development of habituation, considered as a specific type of learning and memory process. To one degree or another, Mf, Anc and Eucl cancel this effect of Mz.(ABSTRACT TRUNCATED AT 250 WORDS)