Stimulation of glycolysis accompanies a rise in pH in intact polymorphonuclear leukocytes and supernatant preparations derived from homogenates of these cells. The curve of lactate production plotted against pH for the cell-free system was steepest between pH 6.5 and 7.0. Our studies indicate that phosphofructokinase is the key control point, and a secondary locus of control may be at glyceraldehyde phosphate dehydrogenase or diphosphoglycerate kinase. The over-all effect of pH on glycolysis appears not to be dependent on the concentrations of cofactors known to affect phosphofructokinase. In the case of inorganic phosphate, the concentration of neither the monobasic nor the dibasic species is involved in the effect of pH.