Some aspects of the toxic effects of nickel were studied in a toxicological experiment for one year on male albino rats, administered perorally nickel in doses 0.0005, 0.005, 0.05 and 0.5 mg/kg, corresponding to 1/10 of the Soviet MAC respectively, MAC, 10 MAC and 100 MAC of nickel in potable waters, by the following indices: behaviour and general condition of the animals, body weight, weight coefficient of organs; total protein, blood sugar, glucose-6-phosphate dehydrogenase and lactate-dehydrogenase on serum; hemoglobin and erythrocytes in blood. The chronic nickel intoxication in doses of 0.5 mg/kg was established to lead to disorders in protein metabolism and reduction of body weight, in doses of 0.005, 0.05 and 0.5 mg/kg--to disorders in carbohydrate metabolism, erythrocytosis and hyperhemoglobinemia, and in doses of 0.0005 mg/kg--no changes have been established as regards all indices studied.