Immunocytochemical methods were used to localize the gamma-aminobutyric acid (GABA) synthesizing enzyme glutamic acid decarboxylase (GAD) in normal and partially deafferented dorsal lateral vestibular nucleus (dLVN) of the rat. Normal dLVN exhibited more intense staining than the ventral part of the nucleus (vLVN), and this was mainly due to more numerous GAD+ axon terminals surrounding dLVN somata and within neuropil. Small GAD+ somata were also present. Electron microscopy suggested the existence of two types of GAD+ synaptic terminals. The major type conformed to descriptions of Purkinje cell terminals, whereas the minor type did not. Ablation of the anterior cerebellar vermis resulted in a 73% reduction in the number of GAD+ terminals, the percentage decrease being greater around neuronal somata (83%) than within neuropil (70%). The presence of GAD+ somata within the nucleus and the persistence of some GAD+ terminals after extensive lesions of the Purkinje cell afferents suggest that both extrinsic and intrinsic GABAergic neurons may contribute to information processing within the dLVN.