Changes in the contents of blood metalloproteins with prooxidant (plasma cytochromes b558 I and b558 II, erythrocyte membrane cytochromes b558 III and b558 IV, superoxide-producing plasma lipoprotein suprol, and cytochrome b5 from soluble erythrocyte fractions) and antioxidant activities (Cu,Zn-superoxide dismutase, catalase, ceruloplasmin, and transferrin) depended on the duration of hypokinesia (5, 10, and 15 days). The content of metalloproteins, particularly cytochrome b5 and ceruloplasmin, increased at the initial stage, but decreased at later stages of hypokinesia (except for cytochrome b5 concentration, which continued to increase).