[3H]quinuclidinyl benzilate ([3H]QNB) binding to muscarine acetylcholine receptors (mAchR) was measured in cerebral cortex and caudate nucleus of rats at the ages of 7, 14, and 21 days, which had received a subconvulsive intraperitoneal dose of monosodium L-glutamate (MSG) (4 mg/g) on postnatal days 1, 3, 5 and 7. MSG treatment determined an increase of mAchR density in cerebral cortex. This was 8, 15 and 25% at days 7, 14 and 21, respectively. In caudate nucleus, a significant increase of mAchR density was detected at day 7 (240%). However, on postnatal day 14, mAchR binding in caudate nucleus of MSG-treated rats was only 47% higher, while at 21 days, no changes in mAchR binding were found. When MSG was injected to adult rats, no changes in brain mAchR density were detected. Data suggest that early administration of MSG affects the development of mAchR in cerebral cortex and caudate nucleus, whereas the adult brain cortical cholinergic transmission is not sensitive to parenterally administered MSG.