The effects of continuous infusion of cholinergic drugs on behavior in normal rats and on impaired acquisition and retention of several behavioral tasks in rats with basal forebrain (BF) lesions were investigated. Physostigmine and oxotremorine were infused continuously with a miniosmotic pump for 3 weeks, and the performance on several different behavioral tasks was examined during the infusion. In normal rats high doses of physostigmine (4 and 8 mg/kg/day s.c.) produced significant changes in general behavior and impaired performance in the Morris water maze. Oxotremorine (0.25-2 mg/kg/day s.c.) had no significant effects on general behavior or cognitive performance in normal rats, although severe cataracts developed at the high dose (4 mg/kg/day). A deficit in motor habituation in rats with BF lesions produced by bilateral injections of ibotenic acid (30 nmol on each side) was improved markedly by the chronic administration of physostigmine (2 mg/kg/day) and oxotremorine (1 mg/kg/day). BF lesions produced severe impairments in acquisition and retention in a passive avoidance task, an active avoidance and the Morris water maze, which was characterized by a marked disruption of retention. The impairment was also ameliorated markedly by the cholinergic drugs, whereas other behavioral impairments were not affected by the drugs. These results indicate that the continuous administration of cholinergic drugs produces a marked improvement of acquisition and retention in rats with BF lesions, and suggest that the impairment in cognitive performance, especially with regard to retention, caused by BF lesions is due to the disruption of the BF-cortical cholinergic pathway.