Cholinesterase inhibitors, such as physostigmine and tetrahydroaminoacridine, have been found to alleviate some of the memory deficits characteristic of senile dementia of the Alzheimer's type (SDAT). Many toxic side effects, however, have been associated with the use of these compounds. Recently, a cholinesterase inhibitor, methanesulfonyl fluoride (MSF), was discovered to have low toxicity, central nervous system (CNS) selectivity, and a long therapeutic duration. The purpose of this research was to determine if MSF (1.5 mg/kg) would be effective in reducing or blocking amnesia induced by various doses of scopolamine (0.2, 0.6, and 2.0 mg/kg). One hundred and twenty-two female Sprague-Dawley albino rats were trained and retention tested in a Y-maze brightness discrimination task. MSF was highly effective in reducing scopolamine-induced amnesia.