The blood counts of 80 patients with depression were examined (50 unipolar, 30 bipolar). Many had reduced numbers of circulating lymphocytes. This abnormality was more common in the unipolar group (52%) than in the bipolar group (27%). When those patients with an abnormal dexamethasone suppression test response in both groups were compared, the relative and absolute lymphocyte counts were significantly lower in unipolars. Although cortisol hypersecretion may reduce lymphocyte numbers it is not yet clear whether the findings can be satisfactorily explained in this way.