Iron-dependent free radical damage to DNA and deoxyribose results in the formation of thiobarbituric acid (TBA) reactive intermediates. 2. These intermediates have been compared chromatographically and spectrophotometrically after incubation with the enzymes xanthine oxidase and peroxidase. 3. Loss of TBA-reactivity occurred in the bleomycin-iron(II) derived products incubated with xanthine oxidase and in a standard solution of sodium malondialdehyde incubated with peroxidase.