1. Simultaneous intracellular recordings were made from pairs of submandibular ganglion cells to examine why each of these neurons is generally innervated by a single preganglionic axon. 2. Impalements made within isolated clusters of two to fifty cells showed that a preganglionic axon typically innervates several neurons within a group. 3. The neurones innervated by a particular axon tended to be intermingled with other neurons; some neurons were innervated by an axon that was not shared by any of their immediate neighbours. 4. These results indicate a mechanism that causes a preganglionic axon to innervate exclusively many of the neurones it contacts, presumably by successful competition with nearby axons that initially innervate the same cells and continue to provide innervation to neighbouring neurones. 5. Re-innervation of adult ganglion cells shows that this mechanism persists or can be reactivated in maturity.