To evaluate anticholinergic effects on cognition and other functions, we studied 60 healthy volunteers in a double-blind crossover trial of two anti-parkinsonian agents, benztropine and amantadine. Benztropine 4 mg/day, but not amantadine 200 mg/ day, impaired free recall and perception of time, and subjects' perception of their own memory impairment was significantly greater with benztropine. Side effects in general were worse with benztropine, particularly such anticholinergic effects as dry mouth and blurred vision, and benztropine decreased measured salivary flow to a significantly greater degree than amantadine. Our findings support the hypothesis that drugs that decrease cholinergic transmission impair storage of new information into long-term memory, but have little effect on retrieval from memory or on tasks involving only immediate memory. Clinically, anticholinergic agents can levy a considerable burden on memory and time perception.