The pathobiology of schizophrenia is poorly understood, and many neuroanatomical domains have been considered to underlie the pathophysiology of the disease. There is considerable clinical and neuroradiological evidence to support cerebellar involvement in the schizophrenic illness. We have analysed the changes in synaptic and cytoskeletal proteins in the cerebellum associated with schizophrenia. The cerebellar expression of tau and MAP2 proteins is similar in schizophrenia to that detected in age-matched controls, whereas the level of SNAP-25 is significantly depleted in the schizophrenic cerebellum. Other synaptic proteins, such as synaptophysin and syntaxin, are not affected. This provides evidence that alterations of the cerebellar synaptic network occur in schizophrenia. These changes may influence cerebellar-forebrain connections, especially those with the frontal lobes, and give rise to the cognitive dysmetria that is characteristic of the clinical phenotype in schizophrenia. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.