Background:Attempt to find changes in the early stages of information processing mechanisms in patients with liver encephalopathy comparing to control group in order to establish markers of the cortex processes impairment. Material/Methods:26 patients were examined,14 of them diagnosed with liver cirrhosis and 12 as the control group (healthy volunteers).In all patients the interview and biochemical tests (ammonia level)were performed.We used passive and active oddball procedure with two kinds of auditory stimuli:standard and infrequent deviant stimuli, differing in physical characteristics. Results/Conclusions:Serum level of ammonia was statistically higher in patients with liver cirrhosis (p=0.0027). experimental and the control group,according to the early cognitive evoked response potentials in response to relevant deviant stimuli.These differences were observed especially at frontal and parietal sites.Absolute value of amplitude of N1 and P2 components were higher in liver encephalopathy group (accordingly: p=0.056, F(1.24)=4.01; p=0.025; F(1.24)=5.71). Value of N1-P2 complex was also significantly higher in the experimental group (p=0.009,F(1.24)=8.07 at the vertex). • These results show differences in early stages of attentive mechanisms of stimuli selection. • Stronger activation observed in liver cirrhosis patients may be considered as higher neural engagement in process of attention