Abstract It was investigated whether the disruptive effects of bilateral lesions of the pedunculopontine tegmental nucleus on two-way active avoidance might vary depending on variations of task demand. The animals were either subjected to bilateral electrolytic lesions of the pedunculopontine tegmental nucleus (Lesion groups) or were sham-operated (Control groups). All the rats were subjected to two 30-trial sessions of two-way active avoidance (separated by ten days), using either a 10-s conditioned stimulus (low task demand) or a 3-s conditioned stimulus (high task demand). The lesions induced a significant disruption of two-way active avoidance in the two conditions tested, but, in both lesioned and control rats, the number of avoidance responses was higher when the 10-s conditioned stimulus was used. In lesioned animals, the condition of high task demand was associated with a significant increase of escape failures. Lesions did not affect locomotor activity during the period of adaptation to the conditioning apparatus, but induced training-specific motor deficits (a decrease of intertrial crossings and an enhancement of escape latencies) regardless of the specific training conditions used. The results are discussed in terms of the influences of the pedunculopontine tegmental nucleus in thalamocortical and striatal systems.