Hydroxylation of aromatic compounds by reduced nicotinamide-adenine dinucleotide and phenazine methosulphate requires hydrogen peroxide and hydroxyl radicals, but not superoxide.

1. A mixture of NADH and phenazine methosulphate hydroxylates aromatic compounds at acidic pH values. 2. Hydroxylation is inhibited by catalase and by scavengers of the hydroxyl radical (-OH) but not by superoxide dismutase. 3. It is concluded that neither O2 leads to nor HO2- is sufficiently reactive to hydroxylate aromatic rings.