Aluminum catalyzes the oxidation of NADH by vanadate both in the presence and absence of a reducing sugar. The effect of aluminum is concentration dependent and inhibitable with superoxide dismutase but not catalase. The fructose-6-phosphate-free reaction is characterized by an initial lag phase which can be eliminated by preincubating aluminum with NADH, but is not altered by preincubating aluminum with vanadate, suggesting that the effect of aluminum is not directly on vanadate. Aluminum also catalyzes vanadyl-mediated oxidation of NADH, and this effect is similarly inhibitable by superoxide dismutase as well as catalase. It is suggested that aluminum catalyzes the oxidation of NADH by vanadium though enhancing the production of superoxide radicals and that this effect may account in part of the biological toxicity associated with aluminum, particularly when associated with the accumulation of other trace elements such as vanadium..