DNA sequences from the mitochondrial cytochrome-b gene were obtained from 41 specimens of Neotoma albigula from the southwestern United States and northwestern México. Phylogenetic analyses depicted that samples of N. a. melanura from southern Sonora and northern Sinaloa formed a clade separate from representatives of the other sampled subspecies of N. albigula (albigula, laplataensis, mearnsi, seri, sheldoni, and venusta). Genetic distances detected between these clades (7.41%) approached divergence levels reported for other sister species of woodrats and indicated that N. a. melanura is presumably a cryptic and genetically differentiated species relative to N. albigula. Analyses of DNA sequences from a nuclear gene (intron 2 of the alcohol dehydrogenase gene, Adh 1-I2) indicated that samples of N. a. melanura formed a separate, monophyletic clade relative to the remainder of N. albigula. Further, habitat, geographic distinctions, and morphological differences were apparent between members of the 2 clades. Together, those data support the elevation of N. a. melanura to species status.