The systematic relationship between Myotis lucifugus carissima and Myotis occultus has been the subject of multiple studies. Although several studies, including a recent allozyme study, concluded that M. occultus is a subspecies of M. lucifugus, this view has not been universally accepted. We reexamined the relationships of these 2 taxa by sequencing the mitochondrial cytochrome-b (cyt-b) and cytochrome oxidase II (COII) genes of specimens from the allozyme study. The results suggest that M. occultus represents an evolutionarily distinct monophyletic lineage and provide support to arguments that M. occultus is a distinct species.