Vitamin B-6-deficient animals exhibit motor abnormalities. To investigate the possible physiologic alterations in the dopaminergic nervous system in vitamin B-6 deficiency, dopamine release in the striatum of vitamin B-6-deficient rats was determined using in vivo electrochemistry. Male Sprague-Dawley rats, 3 wk old, weighing 50-60 g, were randomly assigned to a control (7 mg pyridoxine HCl/kg diet), vitamin B-6-deficient (0 mg pyridoxine HCl/kg diet), or pair-fed (7 mg pyridoxine HCl/kg diet) group. After 8 wk of dietary treatment, plasma concentrations of pyridoxal 5'-phosphate as well as the striatal pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate were significantly lower in the vitamin B-6-deficient group than in the control and pair-fed groups. The dopamine concentrations of the striatum and the magnitude of the dopamine release after local application of KCl did not differ among the groups. However, the time required for KCl-evoked dopamine release to reach its peak level was significantly longer for the vitamin B-6-deficient rats than for controls. In addition, the decay time from the peak to one-half of the KCl-evoked dopamine release was also significantly prolonged in vitamin B-6-deficient rats compared with the control group. The results indicate that the cellular content of dopamine does not reflect the functional state of dopaminergic neurons in vitamin B-6 deficiency. The time course for release of dopamine and decay of the released dopamine is prolonged by vitamin B-6 deficiency, which might contribute to the motor abnormalities of the deficient rats.