Aggregation of human blood platelets by exogenous arachidonic acid is accompanied by a powerful increase in the net flux through the hexose monophosphate shunt and a decrease of the level of reduced glutathione. When platelet cyclooxygenase is inhibited by acetylsalicylic acid diminution by about 60% of arachidonic acid induced flux through the hexose monophosphate shunt as well as lower initial decrease of the glutathione level are found. Investigations with other glutathione oxidizing agents as diamide or tertiary butyl hydroperoxide reveal that acetylsalicylic acid influences neither the activities of glutathione providing enzymes nor that of glutathione peroxidase which catalyzes glutathione consuming reactions in the arachidonic acid metabolism. Together with literature data the results point to a consumption of reduced coenzymes in both cyclooxygenase and lipoxygenase pathways in platelets.