New Zealand's native frogs (genus Leiopelma) are considered to be archaicamphibians of exceptional scientific interest that appear to have remainedvirtually unchanged for 160-200 million years. They are among the rarestextant amphibians and are highly restricted in distribution, confined toisolated, highly disjunct, populations on the North Island and a fewsmall offshore islands in Cook Strait. Previous investigations havesuggested, based on patterns of allozyme variation, that theStephens Island frog (Leiopelma hamiltoni) and Archey's frog(L. archeyi) are sister taxa to the exclusion of the Maud Islandfrog, a species in close geographical proximity to the StephensIsland frog and previously viewed as a population of thisspecies. As a consequence of these data, a new species,L. pakeka, the Maud Island Frog, has been described. This newspecies definition has dramatically enhanced the conservation statusof L. hamiltoni, of which there are probably fewer than 150individuals. In this study we re-examine the systematics of theLeiopelmatidae using mtDNA sequence analyses. Partial 12 Sribosomal RNA and cytochrome b (Cyt b) gene sequences wereobtained for 57 frogs from six populations representing allfour extant Leiopelma species. Contrary to previous reportswe find L. pakeka and L. hamiltoni to be monophyletic. The amountof variation evident between these present species (<1% for Cyt b)is comparable to that seen between populations of L. archeyi. Basedon these data, classification of L. pakeka and L. hamiltoni asseparate species appears to be unwarranted, but they may besufficiently distinct to warrant classification as evolutionarilysignificant units.