In order to determine effects of iron deficiency on the living body, rats were given the iron deficient diet (Group 1, iron content, 0.32mg/100g), the complete diet added with iron (Group 5, iron content, 32.5mg/100g), the diet added with 1% chlorella (Group 2, iron content, 2.2mg/100g), the diet added with 5% chlorella (Group 3, iron content, 7.4mg/100g), or the diet added with 10% chlorella (Group 4, iron content, 13.9mg/100g). For the first 30 days, rats of all groups were given the iron deficiency diet to make them iron deficient, and were subsequently given the respective diet during the next 30 days to observe various changes in the conditions of rats. Following results were obtained. 1) When rats were reared for 30 days with the iron deficient diet, rats of these groups became anemic and their hemoglobin concentrations and hematocrit values lowered. Rats of Groups 3, 4 and 5 fed with the diets containing certain amounts of iron rapidly recovered, while the recovery of those of Group 2 fed with less iron content diet was delayed. Group 1 fed with the iron deficient diet showed no recovery. 2) Examination of effects of these diets on the rats body weight gains revealed that the growth of Groups 1 and 2 with iron deficiency was delayed notably (p less than 0.01) as compared with Group 5 and that of Group 3 was likewise restrained (p less than 0.05). The relative organ weights of all rats were examined. The liver weight in Groups 1, 2, 3, 4 was lower than that in Group 5, while that of the spleen in Groups 1 and 2 was higher than that in Group 5. 3) The Numbers of erythrocyte decreased in Groups 1 and 2 (p less than 0.01) and increased in Groups 3 and 4 (p less than 0.01) as compared with Group 5. There was no direct relation between the iron content in the diet and the number of leukocytes and their compositions. 4) Serum iron decreased remarkably in Groups 1 and 2 (p less than 0.01) but there were no intergroup differences in blood glucose value. 5) When osmotic fragility of erythrocyte membranes was expressed in term of NaCl concentration to indicate 50% hemolysis, Groups 1, 2 and 3 apparently increased their resistance as compared with Group 5 (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)