OBJECTIVE: New-generation antipsychotics have been proposed to normalize the P50 sensory gating index in patients with schizophrenia. In the context of a double-blind comparison of olanzapine and haloperidol, the authors examined the effect of olanzapine on P50 suppression. METHOD: P50 measurements were obtained at baseline while patients were being treated with fluphenazine and after 12 weeks of double-blind treatment with either olanzapine (N=12) or haloperidol (N=12). RESULTS: There were no treatment group differences in P50 amplitude, latency, or sensory gating ratio. CONCLUSIONS: These results suggest that there is not a significant differential effect of olanzapine and haloperidol on the P50 sensory gating index in schizophrenia.