Vital observations were carried on with 33 examples of tumor ascites in tissue culture by means of vital staining and carbon particle phagocytosis and also cytological investigations were conducted with T.P.T reaction. With further studies on the nature and cell composition of ascites the following results were obtained. 1. The average specific gravity of ascites has been found to be 1008-1027, the average protein content 3.36 g/dl., the average cell count 584/㎣, and the composition of cells reveals the increase in the appearance of neutrophils, serous cells and signet ring cells among tumor cell, and these are characteristics of the ascites. By dividing these into two groups, namely one ascites group with the appearance of less than 5 per cent of tumor cells and other with the tumor cell appearance of over 20 per cent, the characteristic traits of ascites might be understood still better. 2. The confirmation of tumor cells and tumorous signet ring cells is taken as a direct indication and cytological peculiarities of other cells are considered to be an indirect indication. 3. As for the direct indication, tumor cells and tumorous signet ring cells are generally stained well with vital staining, and the stainability of the group 2 is better than the group 1. However, that of carbon particle phagocytosis is negative. 4. Cytological peculiarities of their own can be recognized in the vital observations of various cells such as those of adenoma, simple cancer, scirrhus, colloid cancer, hepatoma, coelothelioma. 5. As for the indirect indication, coarse and large granules of various cells can be recognized, and also the acceleration of neutral red staining, phagocytic ability of phagocytes and the appearance of Janus green specific granules as well as enhancement of the neutral red stainability of neutrophils and serous cells can be observed. 6. In T.P.T. reaction tumorous ascites is always positive whereas in other ascites they are negative to this test and therefore, this point proves to be a useful indirect indication. 7. For the distinction between tumorous signet ring cells and phagocytic signet ring cells, both possess their own characteristics of original cells and carbon particle phagocytosis of the former in negative, while the latter is positive.