Compound AF64A, ethylcholine mustard aziridinium ion (0.4-8 nmol) was stereotaxically administered into rat dorsal hippocampus, and neurochemical changes were determined 5 days later. AF64A treatment, over an almost 10-fold dose range, resulted in a significant (up to 70%) decline in choline acetyltransferase activity. In the same tissue samples, Na+-dependent choline transport activity was also lowered, with most decreases ranging between 10 and 50% of controls; however, there was no significant correlation (r = 0.39) between these two parameters. Acetylcholinesterase activity was not affected by AF64A treatment when assayed by either histochemical or enzymatic methods. AF64A reduced acetylcholine levels by 43%, but did not alter norepinephrine content or serotonin uptake. These results demonstrate that AF64A can induce a specific, long-term reduction of cholinergic presynaptic biochemical markers in rat hippocampus. Thus, AF64A can serve as a useful new tool to study the cholinergic system and as an important agent to help develop animal models representing disorders of central cholinergic hypofunction.