Acid and alkaline activity of nucleases of the rats trained with emotional positive or negative reinforcement was estimated in the neocortex, hippocampus, midbrain, and in caudal portions of the brain-stem, using native and denaturated DNA as a substrate. The results showed the total increase in nuclease activity during learning. Nevertheless the dynamics of enzyme activation was different depending on the emotional state of rats during learning. The most active enzyme was found in the caudal portion of the brain-stem.