Ibotenic acid was injected in the lateral geniculate nucleus of cats to investigate the suitability of the technique in studies involving anterograde degeneration in the thalamo-cortical pathway when it is important not to damage fibres of passage at the lesion site. Small injections cause localized degeneration of neuronal somata in the lateral geniculate nucleus, but axons passing through the injected zone remain intact. Degeneration can be localized in visual cortex by light microscopic silver techniques and by electron microscopy. The appearance, density and distribution of degenerating cortical axon terminals is similar to what is found after thalamic electrolytic lesions.