The furans, furfural and methylfurfural, are dietary mutagens that are present in various food products and beverages. AT base-pair-depleted calf thymus DNA was prepared by the action of pea seed single-strand-specific nuclease on native DNA. Compared with furan-treated native DNA, furan-treated AT-depleted DNA showed a reduced rate of S1 nuclease hydrolysis and a reduced formation of single-strand breaks, as determined using an alkaline unwinding assay. These results indicate that furfural and methylfurfural primarily react with AT base pairs in duplex DNA, and demonstrate the usefulness of single-strand-specific nucleases in such studies.