A double-blind controlled study of the effects of vitamin B6 supplementation on premenstrual symptoms was conducted. Fifty-five women who reported moderate to severe premenstrual mood changes participated in the study. Symptoms were monitored prospectively through daily home record-keeping over a one-month baseline period followed by two months of treatment. Subjects were randomly assigned to receive daily supplements of 150 mg of vitamin B6 or placebo over the entire two-month treatment period. Analysis of covariance suggested that even though vitamin B6 may improve premenstrual symptoms related to autonomic reactions (eg, dizziness and vomiting) and behavioral changes (eg, poor performance and decreased social activities), a significant amount of physical and affective symptomatology remained during the premenstrual phase. In light of recently reported, potentially toxic effects of low doses of vitamin B6, our results call for caution in using this therapy for premenstrual symptoms.