The organum vasculosum lamina terminalis (OVLT), the suprachiasmatic nucleus (SCN) and the supraoptic nucleus (SON) are three hypothalamic structures involved in the osmotic and circadian control of neurohypophysial secretion. Recent experiments have suggested that interactions between osmotic and circadian factors may be important for homeostasis. The existence of an in vitro slice preparation retaining these nuclei and their interconnections would therefore be useful for the analysis of synaptic interactions. In the rat, the OVLT, SCN and SON are found at increasingly ventral and lateral positions along the rostro-caudal axis, such that conventional 400 microm slices taken in the pure coronal or horizontal planes do not retain all three nuclei. Here we show that horizontal slices cut at angles of 38-42 degrees relative to the dorsal surface of the cortex retain large fractions of the three nuclei. Intracellular recordings revealed membrane properties consistent with those previously published for OVLT, SCN and SON neurons. Moreover, antidromic and synaptic responses evoked by electrical stimulation revealed that extensive axonal projections are retained between these nuclei. Finally, chemical and osmotic stimulation of the OVLT exerted powerful influences on the rate of spontaneous synaptic events in SON neurons. We therefore conclude that angled horizontal hypothalamic slices represent a useful preparation for the analysis of physiological interactions between the OVLT, SCN and SON.