We have observed increased relative blood flow to the left globus pallidus and evidence for subtle forms of right-sided hemineglect in neuroleptic-naive schizophrenic patients. These findings occur in animals following certain lesions such as unilateral destruction of midbrain dopaminergic neurons, and are presumed to be due to left striato-pallidal hyperactivity. A survey of the literature reveals many similarities between animals with unilateral dopaminergic denervation and schizophrenic patients. It has previously been suggested that available evidence does not preclude the possibility that schizophrenic patients have something like a dopaminergic deficiency. Other studies demonstrate that neuroleptics reverse asymmetries in indices of dopamine turnover. A model based upon dopaminergic hemideficiency is outlined, and can potentially explain other abnormalities in schizophrenic patients including eye movement abnormalities and the link between temporal lobe epilepsy and psychosis. A companion article describes how this model can account for some of the phenomenological symptoms of psychosis.