No consensus has been obtained about blood electrolyte status, especially about magnesium, in affective disorders. This is mainly due to the lack of information about the distribution of the patients in clinical subgroups, sex, type of treatment and about the severity of their illnesses. Most of these studies concerned treated patients. We confirmed in this study that drug-free depressed patients have higher erythrocyte and plasma magnesium than controls, as shown in previous reports. Significant differences are observed in as shown in previous reports. Significant differences are observed in patients for sex and between clinical subgroups. Low plasma potassium levels are described in both male and female depressed patients. The erythrocyte magnesium level tends to normalize in parallel with clinical improvement, depending on sex and clinical subgroup, and seems then to be related to the intensity of the depression. Plasma magnesium in male and female patients, except for female unipolars, remains higher than controls in all conditions and might be related to the diagnosis of affective disorders.