~Glucose-6-phosphate dehydrogenase (G6PD; D-glucose &phosphate:NADP+ oxidoreductase, EC 1.1.1.49) has been purified from AspergiZZus nidulans and AspergiZZus niger by a combination of affinity and anion exchange chromatography. A 500-1000-fold purification was obtained and the final enzyme preparations were shown to be pure but not homogeneous. For both fungi the purified enzyme preparation gave two bands on native and denaturing gels. The catalytically active form is a multimer. The molecular mass of the monomers is 60 and 57 kDa for A. nidulms and 55 and 53 kDa for A , niger. Both enzymes exhibited strict specificity towards both substrates glucose 6-phosphate and NADP+. The A . niduZans and A . niger G6PD enzymes catalyse the conversion of glucose Gphosphate via a random order mechanism. Inhibition studies provided evidence for the physiological role of G6PD as producer of NADPH in both fungi.