The carbohydrate metabolism of lung tissue of suckling (1-3 weeks) and adult (40-42 weeks) rats were investigated and compared. The results showed that the apparent km for in vitro glucose utilization was 3,13 mM for adult lung and the V max 136,99 μmol/g/h. This could not be determined for neonatal animals. The rate of glucose entry into the glycolytic pathway of adult lung was faster than in the lung of neonatal rats. However, glycogen utilization by neonatal lung was faster than by adult lung. The in vitro oxygen consumption of the lung tissue slices of both age groups were the same. It is proposed that the slower rate of glucose entry into glycolysis in lung tissue of suckling rats is due to a different hexokinase isoenzyme profile. It is also concluded that glycogen-glucose plays a major role in lung development.