Relationships among the three extant orders of the Class Amphibia were examined using new DNA sequence data from the mitochondrial 12S ribosomal RNA gene. A total of 33 families of amphibians was compared, including representatives of nine of the 10 salamander families, four of the six caecilian families, and 20 of the 22 frog families. Approximately 380 nucleotides were sequenced in each taxon. Of the 333 sites that were aligned and compared for all taxa, 227 were variable. Phylogenetic analyses of these data support the monophyly of the Lissamphibia and the monophyly of each of the three orders, with the Caudata and the Gymnophiona as sister groups. Within the Anura, these molecular data also support the monophyly of the two suborders Archaeobatrachia and Neobatrachia. Although this study represents the broadest sampling of amphibian families at the molecular level, statistical confidence in the relationships must await additional sequence data.