The effects of either intraperitoneally (i.p.) or intrastriatally administered sufentanil on the release and metabolism of dopamine (DA) in the rat striatum were evaluated using in vivo microdialysis. Dialysate concentrations of DA and its acidic metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were increased following i.p. administration of either clinical anesthetic (20 microg/kg) or clinical analgesic (1 microg/kg) sufentanil doses. In addition, sufentanil also increased uric acid concentrations. In contrast, dialysate ascorbic acid and glutamate concentrations were unaffected. Intrastriatal infusion of sufentanil (250 nM) induced only a short lasting decrease in dialysate DA. Subcutaneous naloxone (1.0 mg/kg) abolished sufentanil-induced increases in dialysate DA, DOPAC+HVA and uric acid; however, naloxone (0.1 mM) failed to affect these increases when infused intrastriatally. These results demonstrate that sufentanil, at clinical doses, increases striatal DA release and oxidative metabolism of both DA and xanthine acting at extrastriatal sites with a mu-receptor-mediated mechanism.