The vanadium content of hair, whole blood, serum and urine was estimated by neutron activation analysis in samples from manic patients, depressed patients, recovered manic patients, recovered depressed patients and normal controls. The results suggest that manic patients have significantly raised vanadium levels in hair which fall towards control levels with recovery, but there are no significant differences in the mean vanadium content of whole blood or serum. In contrast, depressed patients have raised levels of vanadium in whole blood and serum which appear to fall with recovery. Levels of vanadium in serum correlate strongly with those in whole blood, but neither shows significant correlation with vanadium in hair for either patients or controls. Hair and blood probably serve as indicator tissues for differing aspects of vanadium metabolism.