To examine psychophysiological features of MAP psychosis and schizophrenia, P300 component of event-related potentials during an oddball paradigm were recorded in 25 MAP psychotics and 25 schizophrenics. P300 component was evaluated using baseline-to-peak measurement and principal component analysis. P300 amplitude in MAP psychotics was smaller at Fz and Cz region than in the controls. Unlike schizophrenics, P300 amplitude in MAP psychotics was not smaller at Pz region than in the controls. P300 latency in MAP psychotics and schizophrenics were delayed. These results indicated that MAP psychotics have some biological changes in their central nervous system after the remission of acute psychotic state.