Phagocytosis of leucocytes in the blood of acatalasemia for carbon particles was investigated by means of the slide method, using the blood of healthy people and various oto-rhino-laryngological patients as controls. Phagccytosis in neutrophils was classified into five degrees from negative to 3 positives (-, ±, +, ++, +++), giving them values of 0, 1, 2, 3 and 4 respectively, according to the degrees of phagocytosis. The mean values counted by this method were as follows; 1) Number of healthy people examined was seven and the mean value was 2.55. 2) Nineteen otorhinolaryngological patients were examined and their mean value proved to be 2.50. The mean value of thirteen out of these nineteen patients was 2.54, except six cancer patients. Three out of these six cancer patients had been treated with radium and the mean value did not differ from that of healthy people, while three X-ray treated patients showed the mean value of 2.31. 3) Number of acatalasemia patients was two and their mean value 2.53. As far as the present experiment is concerned, there appears no significant difference in the degree of phagocytosis in leucocytes for carbon particles in the groups examined except X-ray treated cancer patient group, who showed lower mean value.