The rate of erythrocyte glycolysis of blood from normal volunteers was 12.0 mg.% glucose consumed/hr with 5 x 106 Rbc/cu.mm. The mean glycolytic rate of blood from tumor patients (14.5 mg.% glucose consumed/hr. with 5 x 106 Rbc/cu.mm.) and from patients with other chronic diseases (17.4 mg.% glucose consumed/hr. with 5 x 106 Rbc/cu.mm.) was found to be greater to a statistically significant degree than that of normals in the absence of reticulocytosis. This suggests that the red cell population of the patients with neoplastic and chronic diseases may be younger than that of normal subjects and that only some of the young cells have demonstrable reticulum.