One of the performance features that is generally considered crucial to increasing the potential prey spectrum of lizards is bite capacity. In this study we tested whether bite forces may serve as a basis for diet selection in two syntopically occurring lacertid lizards. We did so by measuring bite forces in vivo for a large sample of lizards of the species Podarcis muralis and Lacerta vivipara. To assess the ecological relevance of the bite forces, we tested the hardness of a number of natural prey items of both species. The results of our study support the predictions of biomechanical models of biting in lizards and indicate that both larger animals and larger headed ones bite harder. Surprisingly, head shape is an excellent predictor of bite performance in the species studied. Moreover, it is demonstrated that bite capacity is a potentially important ecological variable that could be used as a factor in explaining patterns of food-resource use, ontogenetic dietary shifts, and sexual dimorphism in diet.