There is a growing body of evidence which consistently suggests that membrane lipid abnormalities occur in major depression.Omega-3 essential fatty acids, in particular docosahexaenoic acid (a member of the omega-3 family), seem to be depleted in depression. Recent prospective studies have confirmed that depression is a major predictor of coronary heart disease and hypertension and is associated with the onset and course of non-insulin dependent diabetes. Polyunsaturated fatty acids are implicated in each of these physical diseases. In view of these findings the way depression is perceived and treated may need to be re-examined.