Histaminergic neurones in the tuberomammillary nucleus possess electrophysiological properties which distinguish them from other neurones in their neighborhood. Their resting potential is -50 mV and they are spontaneously active at about 2 Hz in a slice preparation. They display a transient outward rectification and an anomalous inward rectification. Bath application of galanin (0.1 microM) reduced their firing rate significantly and hyperpolarized them slightly.