Efforts to conserve the endangered Stephens' Kangaroo Rat have been complicated by its morphological similarity to the sympatric Pacific Kangaroo Rat. We used discriminant analysis of a variety of morphometric characters to develop a protocol for distinguishing these two species in the field. The species differ significantly in skull, hair, and external metric characters measured on live specimens. Discriminant analysis indicated that the two species can be distin- guished more successfully on the basis of weight, ear length, and head shape than on the basis of hair characters alone. We outline a simple and effective protocol for identifying live-captured specimens using ear length and postorbital head width.