Deficits in sensorimotor gating as assessed by prepulse inhibition (PPI) of the startle reflex have been reported in schizophrenia. However, the state or trait nature of these deficits and the relationships with clinical features and psychopathological symptoms are not clear. To explore these issues, we performed a longitudinal study with schizophrenia inpatients. We examined 36 medicated schizophrenia inpatients twice in the course of an acute psychotic episode: recently after admission and after psychopathological improvement 2-3 weeks later. In addition, we examined 18 healthy control subjects twice (two weeks apart). Relative to control subjects, patients with schizophrenia had lower PPI only in the acute, but not in the improved clinical state. Larger PPI deficits were associated with more severe formal thought disorder and bizarre behavior. In the present longitudinal study, PPI deficits in schizophrenic patients appeared to be state dependent. Taking into account recent evidence from the literature we propose that reduced PPI may be a mediating vulnerability marker of schizophrenia: Impairments in sensorimotor mechanisms which subserve PPI of the startle reflex may both predispose individuals to develop psychosis, and, in addition, may covary with the presence of acute positive symptoms.