Patients with schizophrenia exhibit deficits in an operational measure of sensorimotor gating: prepulse inhibition (PPI) of the startle response. M100907, a selective 5-HT 2 A -receptor antagonist that has been developed for clinical testing as an antipsychotic in schizophrenic patients, has been tested in several animal models of the gating deficits in schizophrenia, including PPI. Previous studies have shown that M100907 blocks or reduces the disruptive effects of hallucinogenic 5-HT 2 agonists (e.g., DOI) and psychotomimetic NMDA antagonists (e.g., phencyclidine) on PPI. In the present paper, we report the results of three studies conducted to determine the effects of M100907 on apomorphine-induced disruption (one experiment) and isolation rearing-induced disruption of PPI in rats (two experiments). Results showed that M100907 failed to reduce the disruption of PPI caused by the dopamine agonist apomorphine. Nevertheless, M100907 partially reduced the disruption of PPI caused by isolation rearing. Thus, M100907 shows efficacy as a putative antipsychotic in nondopaminergic PPI models of the sensorimotor gating deficits in schizophrenia. [