Red cell glycolytic intermediates and adenosine triphosphate were evaluated in term infants from birth to one year of age and compared to values obtained from normal adults and subjects with a population of a similar mean cell age. The concentration of glycolytic intermediates, with the exception of phosphoenolpyruvate were elevated at birth when compared to normal subjects, consistent with a young mean red cell population. The mean levels of red cell glucoses-phosphate, fnictose-6-phosphate, and “total triose phosphate” were elevated on days 1 and 4 of life when compared to both red cells from normal adults and subjects with a similar young mean red cell age. Glucose-6-phosphate steadily increased in concentration, peaked at 3 to 4 wk of age, and then progressively decreased in value. Total triose phosphate declined to a mildly elevated concentration by 3 to 4 wk of age. The mean concentrations of 2,3-diphosphoglycerate and adenosine triphosphate were normal on day 1, increased on day 4, and then declined by 3 to 4 wk to normal values, until 5 to 6 months when both increased. The mean phosphoenolpyruvate concentration was decreased on day 1 of age when compared to red cells of a similar mean age, but this decrease was not significant (P> 0.05).The mean concentrations of 3-phosphoglycerate and 2-phosphoglycerate were normal for mean red cell age on day 1 of life. The concentration of 2-phosphoglycerate increased at 3 to 4 wk of age and remained elevated for cell age at 11 to 12 months but this increase was not statistically significant (P> 0.05). 3-Phosphoglycerate levels did not change significantly throughout the first year of life. At one year of age, all red cell glycolytic intermediates and adenosine triphosphate were elevated when compared to red cells from normal adults, but were comparable to those observed in subjects with a red cell population of a similar mean cell age, consistent with the persistence of a young red cell population throughout the first year of life.SpeculationThe pattern of glycolytic intermediates in the first year of life is suggestive of a relative “block” in glycolysis at the phosphofructokinase step. This block appears to result from factors other than decreased enzyme activity alone and may be secondary to an enzyme with altered kinetic properties and/or the influence of extracellular factors on enzyme activity at thein vivolevel.