In previous studies we have shown that aspiration lesions centred on lobule HVI in the cerebellar cortex of rabbits produce a profound loss of conditioned nictitating membrane (NM) responses. Because aspiration lesions of the cerebellar cortex cause retrograde degeneration in precerebellar nuclei we tested in rabbits whether excitotoxic lesions of the cerebellar cortex that spare these precerebellar nuclei also cause a loss of conditioned NM responses. Following discrete injections of kainic acid into HVI and rostral regions of the adjacent folia of crus I and crus II, we observed an immediate loss of conditioned NM responses. Following extensive retraining several subjects showed a gradual recovery of conditioned responses. But subjects with the most complete lesions never recovered more than a few conditioned responses. Kainic acid lesions did not change ipsilateral unconditioned reflex responses to a range of stimulus intensities. The kainic acid injections caused obvious degeneration of Purkinje and granule cells but not of the precerebellar nuclei. We conclude that HVI and parts of crus I and crus II are essential for normal retention of conditioned NM responses.