Effects of dietary iron deficiency on growth, the distribution of hemoglobin (Hb) at rest and during exercise, the characteristics of muscle fiber types, and glycogen depletion patterns were studied in newly weaned male mice. Forty-eight mice were randomly divided into iron-deficient and control diet groups. Severe iron deficiency impaired general growth, but growth was restored following iron repletion. The mean +/- SEM blood Hb concentrations at rest after 7 weeks were 5. 8 +/- 0 VSports手机版. 7 and 12. 5 +/- 0. 3 g/dl in iron-deficient and control groups, respectively. The mice fed iron-deficient diet for 7 weeks had an increased Hb level of 10. 9 +/- 0. 5 g/dl 1 week after an i. p. injection of Imferon (1. 25 mg Fe). The Hb contents in brain and gastrocnemius as well as whole body were lowered by iron deficiency. Iron-deficient anemic mice tended to increase the percent distribution of Hb to brain during exercise. This value was significantly greater than in control and iron-treated groups. The iron-deficient group had relatively less glycogen than controls, but no significant tendency in glycogen depletion pattern was observed in any fiber types. It is suggested that decreased Hb content in working muscles due, in part, to greater distribution to brain could be one of the limiting factors for work performance in anemic individuals. It is further suggested that decrease in oxidative muscle fibers as well as the decreased concentration and/or activities of oxidative substances may also be one of the limiting factors. .