The effect of tetraethylthiuramdisulfide (disulfiram) on the catabolism of dopamine within discrete regions of the brain was investigated in the unrestrained rat. After a guide cannula had been implanted stereotaxically, a given subcortical site was radiolabeled with 14C-dopamine (DA) by microinjecting 2.0 mu Ci in 2.0 microliters. Successive push-pull perfusates collected from each tissue were assayed by paper electrophoresis for the separation of DA metabolites. When disulfiram, a potent aldehyde dehydrogenase (ALDH) inhibitor, was given intragastrically in a clinically efficacious dose of 200 mg, the formation of the acids DOPAC and HVA was inhibited within perfusates of the caudate nucleus and nucleus accumbens. However, following disulfiram treatment, the proportion of alcohol metabolites did not differ from the control level in the untreated rat. The level of ALDH decreased by approximately 50% in these subcortical nuclei following the inhibition of the enzyme by disulfiram. Conversely, in samples of perfusate obtained from 14C-labeled sites within inferofrontal cortex, periform cortex, diagonal band of Broca, lateral-posterior caudate nucleus, tuberculum olfactorium, lateral olfactory tract or the olfactory nuclear complex, the proportion of DA metabolites remained stable. Generally, a low rate of deamination of the exogenously injected DA occurred within perfusion sites in the ventrobasal forebrain, whereas an intermediate rate of deamination was noted in samples collected at more dorsal loci. Thus, clearcut regional differences in DA catabolism occur in the brain of the living animal, which may depend upon the characteristics of the dopaminergic-rich area of the rat's brain.