A simple microfluorometric method is described for measuring glucose-6-phosphate dehydrogenase (GPD) and 6-phosphogluconate dehydrogenase (PGD) activities in human erythrocytes. Only 50 µl of whole blood is required. The cells are lysed with digitonin and the rate of NADPH generated in the enzymatic reactions is followed kinetically with a recording fluorometer. GPD activity is measured by subtracting the PGD activity from the combined activities of GPD and PGD. A correction is made for the quenching effect caused by hemoglobin. The entire analysis requires less than 1 h. No significant sex-related difference was observed. Both enzymes are stable at 30°C for seven days in samples collected either with heparin or in Alsever’s solution.