Red deer (Cervus elaphus) and roe deer (Capreolus capreolus) are 2 of the most numerous wild ungulate species in Europe. They are sympatric over a large part of their total geographic range. There are no reliable techniques for differentiating between them when studies are based on hair or fecal sampling in the field where the 2 species’ ranges overlap. Here we describe a test for differentiating between red and roe deer hair samples using the polymerase chain reaction (PCR) method by amplifying a section of the mitochondrial DNA D-loop, which differs in length between species