Studies have been made of the effects of metabolic inhibitors on the oxidation and incorporation of radioactivity into nucleotides of glucose labelled in the 1, 2, and 6 positions. The results indicate that in Ehrlich ascites carcinoma cells the predominant oxidative pathway is the hexosemonophosphate shunt. Investigation of the time courses of oxidation of the labelled glucose molecules confirms this conclusion. The pattern of incorporation of radioactivity initially suggests that nucleotide ribose is not formed via this pathway. However, it is shown that the coupling of an active transketolase system with the other enzymes of the hexosemonophosphate shunt provides a sufficient explanation of all the experimental observations. The conclusion is reached that pentose is formed by oxidation of glucose through the shunt but that the labelling pattern is largely established as the result of the exchange reaction catalyzed by transketolase.