An NAD(P)H oxidase-like activity was found in semisynthetic flavoadducts, prepared from an aldehyde derivative of riboflavin and commercial poly(vinylalcohol) (PVA), previously grafted with aminopropyl side chains. Both water-soluble and water-insoluble beaded preparations were obtained. The products showed a noticeable NAD(P)H oxidase-like activity, converting the nucleotide substrate to its oxidized counterpart NAD(P)(+) at the expense of molecular oxygen, the latter being reduced to hydrogen peroxide. In contrast to some "true" beta-NAD(P)H oxidases, the PVA adducts do not require the presence of additional flavin adenine dinucleotide (FAD) to work; some properties of the flavoadducts were studied that make these flavoadducts good candidates for technological applications.