Schizophrenic patients on the same hospital diet as control group subjects had significantly lower levels of fasting plasma vitamin C (p less than 0.05) and 6-hr urinary vitamin C excretion after an ascorbic acid load test (p less than 0.01). After administration of 70 mg of ascorbic acid for 4 weeks there was no longer any difference in plasma vitamin C levels between schizophrenics and control group subjects, but the urinary vitamin C excretion after the vitamin C loading test remained significantly lower in schizophrenics (p less than 0.05). The administration of 1 g ascorbic acid for 4 weeks, in addition to eliminating differences in the plasma vitamin C level, also increased the urinary vitamin C excretion of schizophrenic patients to the level of the control group subjects. The results of this study are in agreement with the hypothesis that schizophrenic patients require higher levels of vitamin C than the suggested optimal ascorbic acid requirement for healthy humans.