We expand on our initial reports of reduced mismatch negativity, MMN, (1991a ) and negative difference, Nd, (1991b) in schizophrenia by looking at the different representation of these indices of automatic and controlled processing of information in subgroups manifesting paranoid or nonparanoid schizophrenia. Methods: Using a 3-tone auditory oddball (standard 0.8 kHz, deviant 2.0 kHz and 1.4 kHz as deviant in a passive and target in an active presentation), subtraction waveforms for the frequency-deviant MMN, for 1.4 kHz Nd (active - passive) and P300 in both waveforms were studied. Subjects were 22 patients with schizophrenia (mean age 18y) separated into paranoid and nonparanoid groups by a median split of the SANS-SAPS ratings; 11 age-matched OCD and 22 healthy controls were also studied. Results: 1/ MMN amplitude was reduced in both groups of patients with schizophrenia - and more clearly so in the nonparanoid group (by up to 75% around 200 ms after the tone). 2/ Nd showed a delayed onset in the paranoid group. The nonparanoid patients showed a normal onset but longer Nd duration. 3/ P300 amplitude was clearly reduced for the nonparanoid group in both the deviant and target-derived difference waves, while in the paranoid group it was impaired only in the discrimination condition. Conclusions: Difference waves reflecting perceptual deviance (MMN) and a difference of meaning (Nd) are differentially affected in schizophrenia (amplitude and latency differences respectively) and between subgroups of schizophrenia, with the nonparanoid group being the more impaired.