In his clinical and experimental observations on Heinz bodies in various diseases in the field of oto-rhino-laryngology and acatalasemia the author obtained the following results. 1. The mean estimated value of Heinz bodies in normal persons has been 61 ‰ in male and 73 ‰ in female. 2. In chronic sinuitis and chronic otitis media an intermediate acceleration in Heinz body fomation can be seen and only a mild acceleration in chronic tonsillitis. However, no significant fall in the hematocrit value can be recognized in any of these cases. 3. In the patients with cancer in the field of oto-rhino-laryngology the advanced acceleration in the Heinz body formation can be recognized, at the same time the hematocrit value reveals a considerable fall in a reverse proportion to the acceleration. 4. In acatalasemia despite the hematocrit value being within the normal range, the formation of Heinz bodies reveals the highest acceleration. 5. The increment in Heinz bodients in the patients gradually begins to fall after the operative removal of lesions and returns to the normal level, while in the case of malignant tumor it hardly declines even after the removal of tumor. 6. In the estimation of Heinz bodies, the higher acceleration can be recognized in the case where catalase in blood is decreased rather than in the case of anemia. 7. when HCl-hydroxylamine is made to act on pigeons and ducks, having an extremely small amount of catalase in blood, and hens and rabbits supposedly to have normal amount of blood catalase, pigeons show the most marked increment in the Heinz body formation, while on the other hand no significant acceleration can be recognized in hens. 8. When hydrogen peroxide (H(2)O(2)) solution is made to act on the blood of the four animals mentioned above, the acceleration in the Heinz body formation is most striking in pigeons followed by ducks, rabbits, and hens in that order, showing an extremely mild formation of Heinz bodies in hens. 9. In the daily examinations of the blood in the pigeons and hens injected continuously with H(2)O(2), the pigeons reveal a marked increment in Heinz bodins, showing about 87 per cent of the blood, while hens an increase of only about 35 per cent of the blood tested. 10. In the daily examinations of the blood of the pigeons given successive injections of HCl-hydroxylamine the Heinz body formation can be observed far more promptly than in the case of H(2)O(2)-injections in almost 100 per cent of the blood tested. 11. In the daily estimation of Heinz bodies in the blood of the animals receiving successive injections of H(2)O(2)-solutionor HCl-hydroxylamine, the decrease in Heinz bodies contained in erythrocytes commences on the fourth day after the start of injection and returns to the normal level on about the seventh day. 12. Judging from these results, it seems that the presence or the absence of catalase in blood is closely associated with the mechanism of the Heinz body formation. In other words, it is assumed that blood toxin or blood toxin-like substance induces the change in the blood pH, and because of this the catalase activity is either inhibited or inactivated, and it is gradually led from oxidative degeneration of blood components to the formation of Heinz bodies.