In 6-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), uric acid, glutathione (GSH) and 1-methyl-4-phenylpyridinium ion (MPP+) were determined by HPLC in the crude striatal synaptosomal fraction after single injections of MPTP 35 mg/kg i.p. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced a 32.5% death rate within 15 min to 10 h. Groups of surviving rats were sacrificed 1, 3, 8 and 24 h after MPTP. MPTP significantly increased levels of DHAA and uric acid and decreased levels of DOPAC and GSH. Individual synaptosomal levels of MPP+ were correlated inversely with DOPAC (r = -0.601, P < 0.002) and GSH levels (r = -0.496, P < 0.02) and directly with levels of uric acid (r = +0.627, P < 0.001); these latter, in turn, were correlated with DHAA (r = +0.418, P < 0.05) and GSH levels (r = -0.357, P = 0.07). In conclusion, the response of the endogenous antioxidant system (increase in AA oxidation, decrease in GSH levels) correlates well with the MPTP-induced increase in uric acid levels and provides further evidence for a mechanism of MPTP neurotoxicity involving oxidative stress produced by xanthine oxidase.