Organotypic cultures of histaminergic tuberomammillary (TM) neurons were grown using explants obtained from newborn rats. The cultures were examined after immunohistochemical localization of the histamine synthetic enzyme, L-histidine decarboxylase (HDC). The morphological properties of the somata, dendrites and axons of HDC-immunoreactive TM neurons in organotypic culture were virtually indistinguishable from those seen in situ. Extensive plexuses of HDC-immunopositive axons, including growth cones, were seen within the hypothalamus, the plasma surrounding the explant and co-cultured hippocampus. Organotypic cultures of TM histamine neurons, and co-cultures with their targets, provide a useful model system for studying several aspects of central histaminergic neurobiology.