Fffects of 8 photosensitizing dyes added to bone marrow tissue culture in cover slips on the wandering velocity and vital staining of intramedullary pseudoeosinophils were studied in comparison with those in culture without the addition of dyes; and the following results were obtained: 1. When photosensitizing dyes such as NK 15, 2, 19, 9, 325, 91, and 243 are added in the solution of low concentration either at 1×10(-5) mole or at 1×10(-6) mole, the wandering velocity of pseudoeosinophils is accelerated, particularly marked are the effects of NK 2, 19, and 243. On the other hand, NK 79 markedly diminishes the wandering veloity; and when it is added in a form of highly concentrated solution, pseudoeosinophils stop the movement in a short time. 2. When NK. 15, 79, 19, 9 and 325 are added in a highly concentrated form of slution in the determination of neutral-red, cells are found highly stained and again fading in color early. This fact in dicates the lowering of cell activity. When NK. 243, 19, 2, 9 and 15 are added in the form of a low concentration, the stainability to vital staining is lowered, suggesting the greater activity of cell function than that in the culture without addition of dye. 3. The fact that NK. 2 and 243 promote the function of pseudoeosinophils coincides well with the acceleration of the growth of bone marrow tissue by dyes.