Although neuroleptic drugs have proven value in the management of patients with schizophrenia, the existing drugs are far from ideal. The pharmacological profile of olanzapine (LY 170053, Lilly) in animal models suggests that it may be an effective antipsychotic drug in humans, with the potential for a reduced incidence of desirable extra-pyramidal side effects, compared to existing neuroleptics. The results of this first investigation of olanzapine in schizophrenic patients indicate that it has efficacy as an antipsychotic compound, relieving positive and negative features of schizophrenia. Olanzapine appears to have an acceptable degree of overall tolerability, and may be associated with a low incidence of extrapyramidal tract symptoms. It does not appear to be free of adverse effects on liver function.