Glucose permeability and metabolism were examined in the reticulocytes of pigs made anemic by daily administration of phenylhydrazine for 5-7 days. Blood samples containing 70-90% reticulocytes were fractionated according to their density by centrifugation. The most immature reticulocytes obtained from the top centrifugal fractions possessed a glucose permeation mechanism. The salient features of glucose transport include a) saturable kinetics with Vm ranging from 0.1 to 0.4 mumol/ml cell X min and with Km ranging from 6.6 to 12 mM, b) inhibition by phloretin, and c) countertransport characteristics suggesting that the glucose entry was mediated by a mechanism involving membrane carrier-type transport. In the course of reticulocyte maturation leading to mature red cells, the glucose carrier mechanism was discarded or rendered ineffective, resulting in nonglycolytic mature red cells. Glucose and ribose consumptions in the most immature reticulocytes were 2.5 and 0.75 mumol/ml cell X h, respectively. Concomitant with the diminishing glycolytic ability, ribose consumption was enhanced slightly as the reticulocytes matured to red cells. Dihydroxyacetone, a potent metabolic substrate for the mature pig red cell, was utilized readily by the reticulocytes.