A major controversy of sexual selection theory is whether sexually dimorphic characters used in display by males have arisen through male-male competition, female choice, or both1-4. Here I describe the chorusing behaviour of male natterjack toads (Bufo calamita) and show that the pitch of the advertisement call is an important determinant of male mating success. Playback experiments using synthetic calls show that when males compete for calling sites they use call pitch to assess the body size and fighting ability of their opponents. Although females initiate mating and can potentially choose any calling male, in two-choice playback experiments, they showed no mating preference based on call pitch. Several authors4-6 have suggested that communal sexual displays by males may have a more important role in intrasexual competition than mate choice, but this is the first time that this hypothesis has been tested experimentally by manipulating a signal property important in male display.