The formation of conditioned passive avoidance reaction (CAR) to a single pain reinforcement was studied in rats following electrolytic dissection of the stria terminalis (ST). Total ST dissection did not affect spontaneous motor activity and vegetative manifestations, though it deprived the animals of the ability to choose an adequate motor response when reproducing CAR. Hence, the ST integrity is essential for the formation of the motor component of the conditioned reaction. Separate dissection of the pre- and postcommissural ST components has shown that determining in the CAR formation is the integrity of the postcommissural component which contains fibres afferent for the amygdaloid complex. Dissection of the precommissural component consisting exclusively of efferent fibres did not affect CAR manifestation. The stria terminalis is probably an afferent activating way for the amygdaloid complex which achieves modulation of defensive conditioned behaviour.