Abstract 10.1002/1098-2361(2000)19:6<511::AID-ZOO3>3.3.CO;2-6 The aim of the study was to develop a simple and reliable method for differentiation of the two phenotypic, very similar Eurasian and North American beavers. Hair bulbs were plucked as tissue samples from the fur of living animals. The mitochondrial cytochrome b locus was amplified by polymerase chain reaction and sequenced. The fragments of the two species differed at 44/41 nucleotide sites. RsaI recognised two mutations, resulting in a restriction fragment length polymorphism that seems to be species specific, as could be revealed by the banding pattern. Zoo Biol 19:511–515, 2000. © 2000 Wiley-Liss, Inc.