By performing a series of bone-marrow tissue culture of normal rabbits the author studied the effects of various vitamins on carbon-particle phagocytosis and neutral red vital staining of pseudoeosinophils, and obtained the following results. 1. Cocarboxylase, vitamins B(2) and K have no accelerating effect on carbon-particle phagocytosis of pseudoeosinophils nor any effect on the vital staining, suggesting that these substances have no effect directly accelerating the functions of pseudoeosinophils. 2. Vitamins B(1), B(6) and nicotinic acid in a certain adequate concentration only accelerate the carbon-particale phagocytosis of pseudoeosinophils slightly but no neutral red vital staining effect. 3. With vitamin B(12) and folic acid a marked acceleration of the carbon-particle phagocy tosis and a slight acceleration with FAD and vitamin C can be recognized. Likewise from the standpoint of the neutral red vital staining these seem to possess the accelerating action on the functions of pseudoeosinophils.