The differential effects of haloperidol on dopamine release and its metabolism were investigated in the anteromedial frontal cortex and the caudate putamen using the intracerebral dialysis method in anesthetized rats after single intraperitoneal injections of 0.01, 0.125 and 2 mg/kg haloperidol. The basal levels of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid, collected every 20 min from the caudate putamen, were 22, 7.7 x 10(3) and 5.5 x 10(3) pg/30 microliters, respectively, and were much higher than those from the anteromedial frontal cortex, which were 1.8, 2.6 x 10(2) and 4.6 x 10(2) pg/30 microliters, respectively. There was a clear difference in the time-response curve of dopamine release between the two brain regions after the injection of 0.125 mg/kg haloperidol, but no difference after the administration of the other doses. The measurements of 3,4-dihydroxyphenylacetic acid and homovanillic acid showed a difference between the two brain structures after injection of the other doses. These findings suggest that there is a difference between the anteromedial frontal cortex and the caudate putamen with respect to the regulating mechanism of dopamine release and its metabolism.