The phylogenetic relationships of 17 species of carcharhinid sharks and four other closely related species were examined by allozyme electrophoresis. Genetic data from 38 loci were used in three different techniques of phylogeny reconstruction (including both phenetic and cladistic methods). The two most instructive trees were produced by using maximum parsimony (PAUP) and Distance Wagner procedures. There was evidence that both the genus Carcharhinus and the family Carcharhinidae may actually comprise paraphyletic groups. A number of proposed morphological species groups were shown to also be closely related genetically. These included C. limbatus/C. tilstoni/C. amblyrhynchoides, C. melanopterus/C. cautus, and C. amblyrhynchos/C. albimarginatus. There appears to be a distinct lineage within the Carcharhinidae that may be characterized by the absence of the interdorsal ridge.