Identified neurons in the dorsal lateral geniculate nucleus (dLGN) of the rat were studied using a Golgi/EM procedure in combination with post-embedding GABA immunocytochemistry. The results of this investigation identify clearly the GABA-immunoreactive nature of the two morphologically distinct neuronal populations found within the rat dLGN--thalamocortical relay cells are GABA-immunonegative whilst the putative 'interneurons' are GABA-immunopositive. This immunocytochemical evidence strongly suggests that 'interneurons' synthesize and use GABA to mediate their local inhibitory synaptic mechanisms within the dLGN of the rat.