Protein products of 51 genetic loci were analyzed by gel electrophoresis using extracts of blood and tissue culture specimens from 12 of the 14 extant canid genera. Genetic distances were calculated and used to derive phenetic trees. The results suggest that the Canidae can be divided into several distinct groups. The wolf-like canids are a group that includes species in the genus Canis and Lycaon pictus (African wild dog). Speothos venaticus (Brazilian bush dog) is weakly associated with this group. Based on the calibration of a consensus tree with a fossil date, Canis mesomelas (black-backed jackal) and Speothos venaticus separated first, approximately 6 million years before present (MYBP). Lycaon pictus and C. latrans (coyote) separated from the line leading to C. lupus (grey wolf) and C. familiaris (domestic dog) approximately 3 MYBP. These results suggest that the blade-like trenchant heel on the carnassial tooth has evolved indepen- dently at least twice within the Canidae. Several distinct genetic stocks appear to have led to the extant South American canids. Chrys- ocyon brachyurus (maned wolf) is estimated to have diverged from Dusicyon vetulus (hoary fox) and Cerdocyon thous (crab-eating fox) approximately 6 MYBP. The divergence time of the last two genera is fairly recent (2-3 MYBP) and is coincident with the opening of the Panamanian land bridge. The remaining South American canid included in this survey, Speothos venaticus, is clustered with the wolf-like canids. The Vulpes-like canids are a distinct phenetic group that includes species in the genera Vulpes, Alopex and Fennecus. Their estimated time of divergence from all the other canids, approximately 9 MYBP, is among the oldest within the Canidae. Among the Vulpes-like canids we surveyed, Alopex lagopus (arctic fox) and Vulpes macrotis (kit fox) appear genetically most closely related. Finally, the biochemical data support the generic status of three canid genera: Urocyon, Nyctereutes, and Otocyon. These taxa are not closely related to any of the surveyed canid species. (Allozyme; electrophoresis; phenogram; Canidae; evolution; trenchant heel; South America.)