1) Significant increase in lactate production was observed within 5 min of phagocytosis by leucocytes. 2) Intracellular concentrations of glycolytic intermediates and cofactors were measured at different incubation intervals in order to know about the mechanism controling the glycolytic activity during phagocytosis. 3) Fructose 1, 6-diphosphate tended to decrease within 5 to 10 min of incubation after adding bacteria. 4) According to the 5, 5-dimethyl-2, 4-oxazolidinedione method, it has been found that intracellular pH decreased in the same interval of phagocytosis. 5) A correlation between intracellular pH and glycolytic activity was discussed.