Morphometric variables were analyzed for 119 specimens from 28 localities in New Mexico and Texas to determine whether they can be used to distinguish between individuals of known identity of Perognathus flavus and P. merriami. Multivariate analysis of variance suggested that morphological characters from individuals of these 2 species differed significantly. Discriminant functions analysis produced 5 cranial and 2 external characters (bullar length, mastoid breadth, interorbital breadth, interparietal breadth, interparietal length, tail length, and hind foot length) that differed significantly in these 2 species. A subsequent classification analysis of 55 specimens from 21 localities was performed to test the utility of these characters in identifying unknown individuals, and 87% of the individuals were identified correctly.