The vasopressin and oxytocin cells of the rat supraoptic nucleus fire in characteristic discharge patterns during hormone release. The present paper discusses the possible role of intercommunication between supraoptic neurones in determining these patterns. In contrast to earlier reports, recent electrophysiological and anatomical evidence suggests that strong coupling is not widespread within the nucleus. However, it remains possible that local release of a neuromodulator, perhaps vasopressin itself, may modify the phasic discharge patterns of the vasopressin cells. The neurosecretory cells project to areas outside the nucleus, and also to a few interneurones within the nucleus, which may mediate indirect communication between the supraoptic neurones.