The Post-Imperative Negative Variation (PINV) is an event-related brain potential that has scarcely been investigated experimentally in schizophrenic patients. Four consecutive experiments using a visual delayed matching-to-sample task show that the PINV (1) is sensitive to the ambiguity in the matching process both in schizophrenic patients and healthy subjects, (2) is sensitive to the provisional memory load in schizophrenic patients only, (3) is related to the experimentally induced motor response, and (4) has a frontolateral topography that distinguishes schizophrenic patients and schizotypal subjects from healthy controls. Taken together, these results suggest that the prefrontal cortex or those cerebral structures functionally linked with it contribute to the rising of the PINV in schizophrenic patients.