The author analyzed clinically and statistically 67 cases definitely diagnosed as leukemia by bone-marrow tissue culture in our clinic during the period from January 1954 to October 1957. The results are described in the following. 1. These 67 cases can be divided into 16 cases of acute neutrophilocytic leukemia, 8 chronic neutrophilocytic leukemia, 2 acute basophilocytic leukemia, 12 acute lymphocytic leukemia, one chronic lymphocytic leukemia, 25 monocytic leukemia, and three others, showing an extremely large number of monocytic leukemia as compared with other Japanese statistics, occupying over one third of the whole. For this reason it seems that monocytic leukemia has previously been included in chronic myelogenous leukemia. Furthermore, it is indeed significant that the two cases of acute basophilocytic leukemia have been confirmed by bone-marrow tissue culture. 2. With the exception of the paucity in the number of infant cases, as our clinic is of internal medicine, there are no particular differences with respect to the sexual classification, age distribution and occupational classification. 3. One case (1.5%) having family history of leukemia, 15 cases (22.7%) having family history of cancer, and 2 cases (3.0%) of atomic bomb survivors have been encountered. 4. As for the characteristics of clinical symptoms all the symptoms of acute myelogenous leukemia proceed acutely, accompanied with marked fever and hemorrhagic tendency along with a high incidence of disorders of the digestive, respiratory and circulatory functions. This type also shows albuminuria in 43.8 per cent and glucosuria in 15.4 per cent in urine. On the other hand, the swelling of the spleen, generally accepted as the symptom specific to myelogenous leukemia, can be encountered only in 25 per cent. Acute lymphocytic leukemia on the whole proceeds more slowly than acute myelogenous leukemia. Speaking only of the symptoms at the onset of the disease, it lacks the hemorrhagic tendency, but its characteristic trait is the complaint of the enlarged lymph nodes. It may be natural to expect the enlargement of lymph nodes in practically all cases of this type, but the swelling of the spleen can also be encountered in the majority, showing the enlargement of lymph nodes accompanied with the swelling of the spleen and the liver in well over 60 per cent. The incidence of pain in the bones, though not so high, is more often observed than in other types, and the acceleration of the urobilinogen excretion in urine is also a characteristic symptom. There is no question of doubt that all symptoms of chronic myelogenous leukemia are milder than those of the acute type, nevertheless, anemia can be found in 90 per cent and fever in 60 per cent. From the standpoint of the symptom at the onset, subjective complaint and the symptom actually present, what can be considered the main characteristic of this type, is the swelling of the spleen, observable in nearly all cases and the giant spleen swollen well over 4 finger breadth below the left costal arch can be encountered in over 60 per cent. On the contrary, the cases with the enlargement of lymph nodes is not so abundant. Monocytic leukemia more often commences with hemorrhagic tendency than any other type, amounting to 40 per cent. Although the incidence of this trend decreases in later stage and becomes about the same as in other type of leukemia, it is worthy of note that the incidence of buccal hemorrhage reach as much as 40 per cent at the same stage. What might be considered as most characteristic of this type is that the severity of almost every symptom is intermediate between the acute type and chronic type. In this type the enlarge ment of the lymph nodes is quite frequent, amounting as much as three quarters of all, while the swelling of the spleen can be found only in less than 30 per cent.