MOTOR effects mediated through adenosine A2Areceptors within the caudate-putamen were investigated in rats using bilateral microinfusions of MSX-3 (9 μg in 1 μl per side), a water-soluble phosphate prodrug of the selective A2Areceptor antagonist MSX-2. Blockade of striatal A2Areceptors produced a significant motor stimulation measured by an enhanced sniffing activity. Furthermore, catalepsy induced by systemic dopamine D1(0.75 mg/kg SCH23390, i.p.) or dopamine D2receptor blockade (1.5 mg/kg raclopride, i.p.) was potently reversed. These findings suggest that A2Areceptors within the caudate-putamen are tonically activated by endogenous adenosine and that a striatal A2Areceptor blockade produces motor stimulant effects, in particular in animals with dopamine hypofunction. The present results support the view that A2Areceptor antagonists may be potentially useful therapeutics for the treatment of Parkinson's disease.