The percentage of neurons that are immunoreactive for the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) was determined within: (1) the lateral geniculate nucleus (LGN), (2) the ventrobasal complex (VB) and (3) the antero-ventral nucleus (AV) of the thalamus in the cat. An antiserum to GABA was used to stain GABA-containing perikarya in 1.0 micrometer thick Araldite-embedded sections. Immunostained somata in all three nuclei were invariably smaller than the immuno-negative nerve cells. 27% of all neurons in the LGN, 33% in the VB and 25% in the AV were immunoreactive for GABA.