Freshly-generated hydrogen per- oxide or a solution of peroxide stimulate the direct oxidation of glucose-l-14C to 14C02 by a soluble supernatant fraction (PFS) of poly- morphonuclear leukocytes (PMN). Only the former appeared to enhance the catalatic oxidation of formate by the preparation. Glutathione oxidation and reduction mediates the former reactions. Glutathione peroxidase and oxidized-glutathione reductase are present in PMN of rat and man, but the former is virtually absent in guinea pig cells. It was not found possible to block glutathionemediated stimulation of the shunt in PMN without affecting phagocytosis per se, as followed by sensitive measurements of phagocytic rate, and glycolysis.