Chitin is produced by a variety of organisms using enzymes called chitin synthases and was recently discovered in certain vertebrates. In our ongoing investigations into the presence of vertebrate chitin, we unexpectedly found it within the electrosensory organs, known as Ampullae of Lorenzini, of diverse cartilaginous fishes. We used histochemical reagents, chemical analyses, and enzymatic digestions to confirm our findings. Further, in situ hybridization with a sequence from the little skate ( Leucoraja erinacea ) revealed that chitin synthase expression is localized to cells inside the organs. These findings indicate that cartilaginous fishes endogenously synthesize chitin and beg further investigation into the function of chitin in the electrosensory system.