The formation of alpha-hydroxyethyl radical from ethanol by deermouse microsomes supplemented with NADPH has been demonstrated with the EPR technique of spin trapping with alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN) as the spin trap, in the presence of deferoxamine mesylate. Superoxide dismutase prevented the formation of the radical adduct of the alpha-hydroxyethyl radical in a dose-dependent fashion, causing complete inhibition of radical formation at a concentration of 20 micrograms/ml, while catalase, azide, or azide and hydrogen peroxide had no effect. Boiling the microsomes or omission of NADPH abolished free radical formation. Metyrapone, cimetidine, isoniazid, octylamine, and p-nitrophenol, inhibitors of cytochrome P450IIE1 activity, decreased free radical formation by 24 to 74% at concentrations ranging from 0.05 to 10 mM. The POBN/.CH(OH)CH3 radical adduct signal was also diminished by formate or mannitol, indicating competition by so-called "hydroxyl radical scavengers. "The involvement of trace transition metals in alpha-hydroxyethyl radical formation by deermouse microsomes was demonstrated by a decrease in free radical adduct signal when metal ions were removed from reagents by treatment with Chelex 100 resin. Chelex treatment was effective even though the metal chelator deferoxamine mesylate, which is generally presumed to render iron catalytically inactive, was present in all incubations. Thus, it is concluded that free radical formation from ethanol in deermouse microsomes is mediated by a transition metal- and cytochrome P450-derived superoxide-dependent oxidizing species even in the presence of deferoxamine mesylate.