The effect of Vitamin C in manic-depressive psychosis was assessed by a double-blind, placebo controlled, crossover trial. Both manic and depressed patients were significantly better following a single 3 g dose of Vitamin C than following a placebo. Preliminary results of a double-blind, crossover comparison of normal vanadium intake with reduced intake in manic and depressed subjects are reported. Both manic and depressed patients were significantly better on reduced intake. These results are in keeping with the suggestion that vanadium may be an aetiological factor in manic depressive illness.