The paper deals with the most important pentose phosphate pathway reactions of carbohydrate metabolism in tissues of the liver, spleen, bone marrow and in blood erythrocytes catalyzed by transketolase. Possibilities are also studied for pentose phosphate production in the mentioned tissues in the nonoxidized reaction of the pentose phosphate pathway catalyzed by transketolase. It is established that due to this reaction the possibility of pentose phosphates synthesis in tissues of the liver, spleen, bone marrow and erythrocytes is very small as compared with that in the oxidative reactions of the pentose phosphate pathway. The reaction rate is higher in the reverse direction when utilizing erytrhroso-4-phosphate and riboso-5-phosphate with glycolysis intermediate products formed. It is also shown that erythroso-4-phosphate inhibits greatly the glucose phosphate isomerase activity. Coming from the data obtained the authors suggest that acceleration of the transketolase reaction towards the utilization of erythroso-4-phosphate as well as of synthesis of fructoso-6-phosphate and glyceraldehyde-3-phosphate promotes the transfer of carbohydrate metabolism from the pentose phosphate pathway to glycolysis.