By determining at first the appearance of Heinz's body in man and male domestic rabbits, both normal, with the Yoshida-Kawamura method, and next by investigating the rate of the appearance of Heinz's body in Bikini hydrogen-bomb patients and in the domestic rabbits injected with radio-isotope P(32) as well as in the rabbits exposed to X-ray, the author obtained the following results: 1. Two separate groups of male and female, each consisting of 25 persons, were selected and the rate of the Heinz-body appearance was determined; and as the result, the average rates of the appearance of each were found to be 63.88‰ (male) and 66.52‰ (female) respectively; thus the average value of females was slightly higher. On the other hand, in the 62 normal male rabbits similarly measured, the average value of the appearance of Heinz's body was found to be 22.19‰. 2. In the case of the 7 fishermen passing through the Bikini area and having shown no apparent clinical disorders, the rate of Heinz-body appearance was found to be still high, yet within 3 to 4 weeks after the examination, it returned to normal, paralleling more or less with the change of blood-iron contents, Sideroblastogram, and the results of Bone marrow tissue culture. In view of this, in establishing a criterion of the recovery of these hydrogenbomb cases, it seems that scrupulous daily examinations such as mentioned previously are of urgent necessity. 3. In the domestic rabbits receiving the injection of 100 μc. P(32)/kg, Heinz's body increased 6 hours after the injection but it returned to normal after 20 to 42 days; even then they maintained a high value of blood-iron contents and showed an unmistakable evidence of radio-active substance in the bone as well. Whereas those rabbits receiving the dose of 850 μc. P(32)/kg showed the increase of Heinz's body either 30 minutes or 3 hours after the injection, and after 48 hours and 28 days respectively their values reached close to 1, 000‰ and continuously showing an intermediately progressive trend, they all died. The blood counts of capillary leucocytes in the case of the rabbit No.58 returned to normal 28 days after the injection, but the percentage of capillary leucocytes, the blood counts of erythrocytes, and the bone picture were still abnormal and radio-active substance could be recognized in the bone. Heinz's body, however, did not appear in the control injected with primary potassium phosphate. 4. Among the 6 rabbits suffering from acute X-ray radiation, and the five from chronic, three of the latter and all the acute cases revealed a progressive proclivity to the formation of Heinz's body before their death.