Visual evoked potentials were examined in 50 male schizophrenic patients and 50 age-matched healthy male volunteers during performance of the Continous Attention Test (CAT). In the patients emerged an evident deterioration of attentional processes: much higher index of errors and longre reaction time than in he healthy subjects. On the other hand, in patients the following alternations is evoked potentials were found:(1) in the non-target condition lower amplitudes ofcomponents; left- sided P1, bilateral N1 as well as frontal P3a; (2) a distinct electrophysiological pattern of target detection, consisting of an increase in amplitudes of either N1 or P3a as compared to the response to the non-target stimulus. Electrophysiological features were related to behavioural data. An increase in the amplitude of N1 during detection of the target, as well as a lower non-target amplitude of P3a, correlated with poor CAT performance, while an increase in the amplitude of P3a during detection of the target correlated with relatively shorter reaction time, and showed no correlation with an index of errors. The results suggest an underlying primary hyperarousability at lower stages of visual data processing (up to N1 latency range) accompanied by several secondary pathological and compensatory mechanisms at the higher stages.