It has been established that in well-trained rats sydnocarb (mesocarb) does not exert a considerable effect on the generation of conditioned reflex of passive avoidance (CRPA). On the contrary, in poorly-trained animals sydnocarb significantly improves CRPA indexes at all three stages of its generation. Sydnocarb proved most effective, when injected before training (on day I). The absence of sydnocarb-induced pain threshold decrease in response to electrical pain stimulation suggests a direct drug effect on memory processes.