Rats with electrolytic lesions of the nucleus basalis magnocellularis were compared to sham-lesioned rats in the retention of a continuously reinforced lever-pressing response and in the acquisition and reversal of a visual discrimination task. The muscarinic agonist pilocarpine, in conjunction with the peripheral muscarinic antagonist methyl-scopolamine, was administered in three doses to subsets of each group during acquisition. The lesion interfered with retention of the lever-pressing response. It did not affect the rate of acquisition of the visual discrimination, but facilitated reversal, and increased the number of perseverative errors made by the rats. Pilocarpine's only notable effect was to increase the latency to respond.