Patch-clamp whole-cell recordings were made in the hypothalamic tuberomammillary (TM) nucleus from isolated histaminergic neurons, identified by their expression of histidine decarboxylase. We compared strychnine-sensitive glycine-mediated currents with maximal currents activated by gamma-Aminobutyric acid (GABA, 0.5 mM) which were blocked by gabazine. The maximal glycine response (1 mM) in histaminergic cells with larger somata (25 microm) was about half of the maximal GABA response whereas in the cells with a smaller soma size (19.5 microm) the glycine response was absent or very small. We conclude that histaminergic cells are heterogeneous with respect to their sensitivity to glycine and this correlates with their size.