Little is known about the effects of atypical neuroleptics on cognitive function. In the present paper, an overview is given of studies on the effects of clozapine on cognitive function in schizophrenia. The available evidence suggests a positive effect of clozapine on tasks in which mental speed plays an important role. Also, clozapine may enhance verbal long-term memory and planning ability. Effects on cognitive flexibility, concept formation and visual memory are not clear. Future research will need to examine the precise effects of clozapine on these cognitive functions. Possible mechanisms of clozapine's action with regard to cognition are discussed.