In previous reports, we have observed that blood magnesium was significantly higher in drug-free patients with major depression when compared to healthy controls. This was especially true for erythrocyte magnesium. Furthermore, the most severely depressed patients had the highest intracellular magnesium content, showing that intracellular magnesium rate was related to the intensity of symptoms. We report here the results of blood magnesium measured in 88 major depressed patients as compared to 61 controls. We show that the mean erythrocyte and also plasma magnesium contents are both increased in these patients. We observe that about 40% of male and female patients have a very significant increase (25%) in intracellular magnesium content as compared to controls. However, about 60% of the hospitalised depressed patients have normal values. None of the controls has high erythrocyte magnesium. This is less evident concerning the plasma magnesium. No differences are observed between patients when classified according to the intensity of moral pain or anxiety. In contrast, the patients with mild to high psychomotor retardation score, which is an index of hypoexcitability, have significant higher erythrocyte magnesium values compared with other patients. The results of male patients without psychomotor retardation do not differ from control values. Our study suggests that central hypoexcitability might be related to an increase in intracellular magnesium observed at the peripheral level, keeping in mind that hyperexcitability, as observed in various conditions such as stress and cardiovascular disorders, is frequently associated, in contrast, with a decrease in blood magnesium.