Recently, research into the connection between vitamins and psychiatric disorder, particularly affective changes, has been in the doldrums, with the exceptions perhaps of studies of folic acid and pyridoxine. The best way for research to proceed is first to establish that the association of a vitamin deficiency with a psychiatric disorder is beyond a chance finding. Then, questions should be asked about what mental symptoms it is linked with, and what the other associations (malnutrition, drugs, physical illness, etc) are. Lastly, queries should be raised about whether the association is causal or if the mental symptoms are merely secondary to the anorexia and poor diet so common in mental illness (or whether they are linked in a vicious circle as suggested by Reynolds et al (1971)). These questions became pertinent in the mid-1960s when reliable ways of assaying B vitamins such as folic acid became more generally available. In this review, I present evidence that deficiencies of folic acid, B12, thiamine, riboflavin, pyridoxine and ascorbic acid are not infrequently found in psychiatric practice. It should be remembered, however, that some ways of assaying vitamins are liable to give a larger proportion of spurious low results than other methods (false positives), although the adoption of more reliable ways of assaying vitamins should reduce this.