1. A simplified assay for the flux through the pentose phosphate and the Embden-Meyerhof pathways in the red cell is described. 2. [1-14C]glucose is metabolized to 14CO2 and 14C-anions. 3. 14CO2 is trapped with KOH and residual [14C]glucose and anions are separated by an enzymatic method, which is simpler and quicker than the usual chromatographic method.