Naylor's recent hypothesis that vanadium ‘poisoning’ could be a factor in the severity of manic-depressive illness drew attention to the normal and even essential presence of vanadium in the diet, and in human living tissues. The whole brain may contain only about 45 micrograms of vanadium (Underwood, 1977; 1979), as against 500 micrograms of manganese, 130 μgm selenium, and less than 20 μgm molybdenum—others of the 12 or so essential metals required in traces. We might take copper as the principle trace metal—an important component of over 50 enzymes, including monoamine oxidase and dopamine β-hydroxylase—with a total in the whole man of about 100 mg. In contrast, metals like potassium (140 gm), magnesium (35 gm), iron and zinc (3–4 gm) are not present in traces but in gram quantities. Lithium, present naturally in the body in extremely minute amounts, is raised in therapy to occupy a borderline position in the scale, rather more than copper, less than zinc.