Abstract: The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy. For each quinone the rate law was first order in NADH and first order in quinone. The rate constants varied from 0.0745 to 9220 M-'s-'. Variation of the pH from 6 to 8 gave no change in rate. The use of 4-D-and 4, 4-D2-NADH revealed kinetic isotope effects. The dideuterio data gave ...