Water and electrolyte contents in plasma and red blood cells (RBC) were studied in 46 patients with depressive syndromes of various etiology (bipolar, unipolar, psychogenic) before and after 14 days of imipramine treatment. Initial low RBC sodium levels were characteristic of patients with bipolar depression. A significant increase in RBC sodium was observed after imipramine treatment in a group of good imipramine responders. RBC sodium changes in psychogenic patients after imipramine were different from those observed in endogenous (bipolar plus unipolar) ones. A fall in plasma calcium levels was shown in the course of imipramine administration mostly in patients with favourable response to the drug.