A simple method is proposed to distinguish hexaploid (Triticum aestivum L.) from tetraploid (T. turgidum L., durum wheat) cultivated wheats on the basis of peroxidase isozymes coded by genome D. It can also be used as a 1st step to detect possible contamination by tetraploid genotype mixtures. The peroxidase patterns of endosperm and of embryo plus scutellum found among 349 entries of a durum wheat world basis collection are shown.