Male Wistar rats were trained for active (shuttle-box) and passive (step-down) conditioned avoidance through negative reinforcement. The memory tests carried out on the 24th hour and on the 7th day after the training revealed that the rats trained for active avoidance demonstrated a considerably higher number of avoidance in both tests, compared with the avoidance shown during the training session. The memory tests on the 24th hour and on the 7th day after training for passive avoidance showed that the rats had mastered the task lastingly. The levels of serotonin (5-HT), dopamine (DA) and noradrenaline (NA) in the frontal cortex were determined on the 24th hour and on the 7th day after the training, both for active and for passive avoidance. The 5-HT content was considerably increased on the 24th hour after both active and passive avoidance training, whereas on the 7th day its level was unchanged for both types of training. The DA content was slightly increased on the 24th hour and on the 7th day after active avoidance training, though it was considerably reduced on the 24th hour after passive training. The NA level was insignificantly raised on the 24th hour after active avoidance training, being considerably reduced after passive avoidance training. The observed changes in the cortical levels of 5-HT, DA and NA are probably caused to a certain extent by the different stressors used as unconditioned-reflex stimuli during the training for active or passive avoidance.