Impairment of the dopaminergic system in the brain induced by dopamine-receptor antagonists or by specific neurotoxin terminal lesions results in motor disturbances in rats. In order to specify further the role of the different dopamine pathways in the brain on motor function, the performance of rats trained in an operant reaction-time task was examined after systemic administration of a dopamine-receptor antagonist, alpha-flupenthixol, and after specific destruction of dopamine neurons by 6-hydroxydopamine perfusion into the nucleus accumbens or caudate nucleus. Rats were trained to press a lever and release it as quickly as possible after a light-cue conditioned stimulus (CS). Reaction time was measured from the CS to the release of the lever for each trial. alpha-Flupenthixol (0.2 and 0.4 mg/kg) injected intraperitoneally impaired the reaction-time performance of the rats. While disruption of dopamine activity in the nucleus accumbens did not affect the performance of the rats, lesions of the dopamine terminals of the nigrostriatal pathway in the corpus striatum (59% decrease in posterior striatal dopamine) significantly impaired reaction-time performance. These results show that moderate decreases in dopamine function restricted to the corpus striatum can disrupt sensitive motor performance, and support the hypothesis that dopamine in the corpus striatum has a role in the initiation of complex goal-directed responses.