The formamidine pesticide amitraz (AMZ) produces many behavioral and physiological changes in rats. To explore possible neurochemical mechanisms for the behavioral effects of AMZ, the dose effect and time course of AMZ on motor activity, monoamine oxidase (MAO) and acetylcholinesterase (AChE) activity were examined. For motor activity studies, male Long-Evans hooded rats were tested in photocell activity measurement devices. AMZ produced dose-related decreases in motor activity of rats allowed free access to food and rats maintained at a stable body weight through food restriction. Lowest effective doses of AMZ tested were 1-3 mg/kg, administered 20 min before testing. AMZ appeared to be about 3 times more potent in food-restricted rats, indicating that amount of body fat may play a significant role in the pharmacokinetics of AMZ. Motor activity returned to control levels over 4-5 days after dosing with 100-200 mg/kg AMZ, whereas recovery was evident the day after administration of low doses (1-30 mg/kg). Inhibition of MAO was measured in whole brain of rats sacrificed at various times after dosing with AMZ. Only doses greater than or equal to 100 mg/kg AMZ inhibited MAO, which was measurable within 2 hr after dosing and lasted up to 7 days. (Copyright (c) 1989 by the Society of Toxicology.)