We have studied effects of intraperitoneal administration of anticholinergic drugs on striatal acetylcholine release in association with motor activity in freely moving rats using brain microdialysis. A low dose of atropine (2.5 mg/kg) increased striatal acetylcholine release. A high dose of atropine (5 mg/kg) or scopolamine (2.5, 5 and 10 mg/kg) increased both striatal acetylcholine release and motor activity, while its quaternary ammonium compounds, atropine methylbromide (5 and 10 mg/kg) and methscopolamine bromide (5 and 10 mg/kg), increased striatal acetylcholine release without motor excitation. Scopolamine (2.5 mg/kg) produced no significant change in striatal acetylcholine content 4 hr after the injection followed by perfusion. These results suggest that anticholinergic drugs cause an increase in striatal acetylcholine release which does not always result in the increase of motor activity.