1. Glucose-6-phosphate dehydrogenase (G6PDH EC 1.1.1.49) from mouse liver has been purified 1100-fold by extraction, ion-exchange chromatography on DE-52, absorption chromatography on Bio-Gel HTP and gel filtration through sepharose 6 HR 10/30. The purified enzyme showed a single band in silver stained SDS-PAGE. 2. The native and subunit molecular weight were 117 and 31 kDa respectively. 3. The kinetic studies and the patterns obtained from the inhibition by-products suggest that the enzyme follows an ordered sequential kinetic mechanism. 4. The reduced Km values for the substrates favour the operativity of the enzyme. The "fine control" of the enzymatic activity was exerted by the NADPH, whose Ki is several fold lower than the in vivo concentration.