The number of white blood cells, differential count of the white bolld cells, absolute numder of lymphocytes and the diameters of the lymphocytes were measured in 7 cases of bronchogenic cancer, 10 cases of gastric cancer, 10 cases of hepatoma, 8 cases of malignant lymphoma and 10 healthy, college students as normal control, and the following results were obtained. 1. Leucocyte counts were mostly within the normral range. The exceptions were; 4 cases of hepatoma and 2 cases of malignant lymphoma showed decrease below 5,000 and one case each of hepatoma and bronchogenic cancer showed increase above 10,000. 2. The absolute number of lymphocytes were decreased to below 1,500 per mm3 in 3 cases out of 6. bronchogenic carcinoma, 4 cases out of 10 gastric cancer, 8 cases out of 10 hepatoma and 7 cases out of 8 malignant lymphomas. 3. The differential count percentage of small lymphocytes with diameters below 7.5 microne in gastric cancer cases averaged about 27.9% and in hepatoma about 29.9%, both close to the average of 30.1% in healthy normal controls, but in the lung cancer the average was 20.3%, in malignant lymphomas average of 17.9% indication the definite decrease in small lymphocytes. In malignant lymphomas and lung cancer the percentage of large lymphocytes increased