While increased dopamine activity is central to our current understanding of the pathophysiology of schizophrenia, dysregulation of a single neurotransmitter is unlikely to explain the disorder adequately. It is argued here that the muscarinic aspects of schizophrenia should be reassessed for a number of reasons. These include current evidence that cholinergic modulation affects both positive and negative symptoms, and neuroendocrine and polysomnographic data that suggest an increased muscarinic cholinergic activity in schizophrenia. In addition, the interactions between the dopaminergic and cholinergic systems are becoming better understood and appear to occur especially in regions that are thought to be relevant in schizophrenia. The fact that the highest affinity of clozapine, with its unique therapeutic profile, is to the muscarinic receptor encourages further evaluation. Finally, the use of anticholinergic agents to treat extrapyramidal side-effects and the fact that many antipsychotic agents have intrinsic anticholinergic activity suggest that the role of the cholinergic system in schizophrenia needs to be more clearly delineated.