Using intracellular recordings of medial vestibular nucleus neurones (MVNn) in guinea-pig brainstem slices, the effects of baclofen, a specific agonist of the metabotropic GABAB receptors, were tested on the three main types of MVNn (A, B and B + LTS MVNn) that were previously identified in this nucleus. Regardless of their type, almost all MVNn were hyperpolarized and inhibited by baclofen. These hyperpolarizing effects persisted following either the addition of tetrodotoxin (TTX) in the perfusion medium, or in the presence of a high Mg2+/low Ca2+ solution known to block synaptic transmission. These results demonstrate that all types of MVNn are endowed with postsynaptic GABAB receptors.