North America was divided into 102 geographic blocks, and the presence vs. absence of 173 amphibians recorded for each. The blocks then were clustered, based upon their amphibian faunas, using numerical taxonomic techniques. Results showed the Pacific slope as having by far the most distinctive species assemblage. A secondary boundary separated Canada and the northern Rockies from regions to the east, south, and west with much greater species richness. A longitudinal boundary lay near 100?W, separating eastern species of mesic habitats from assemblages of amphibians distributed through the xeric plains and southwestern deserts. Finally, a lesser biogeographic boundary separated the eastern U.S. along a diagonal line running roughly parallel to the Appalachian Mountains. This study describes biogeographic regions of North America as revealed by the known distributions of its Amphibia. We have applied the techniques of numerical taxonomy to this problem by 1) dividing the continent into numerous geographic blocks, 2) characterizing each block by the amphibians known to occur in it, and then 3) subjecting the blocks to cluster analysis based upon the similarities of their amphibian faunas. Numerical analysis is a potentially powerful biogeographic tool because it facilitates measurement of faunal resemblances among a large number of small areas, and subsequent objective recognition of major biogeographic regions and boundaries (e.g., Hagmeier, 1966; Kaiser et al., 1972; Sneath and Sokal, 1973; Bock et al., 1978). Savage (1960) mapped eight herpetofaunal regions of North America by comparing range boundaries of all reptiles and amphibians together. Adams (1975) described seven U.S. faunal regions based upon the distributions of reptiles. To our knowledge there have been no previous attempts to describe the biogeography of North America based exclusively upon its amphibian fauna, nor have cluster analytical techniques been applied to such a problem.