Eighty patients with heroin addiction, aged from 15 to 20 years (most of them over the age of 16), were examined. The duration of illness was from 6 months to 3 years. The examination was conducted 2-3 weeks after arresting of withdrawal syndrome. In that period, patients had different mental disorders: depressive-dysphoric, neurosis-like, anxiety-hypochondriac, hysteriform and others. The aim of the examination was to find peculiarities of functioning of different cortical regions in the process of appraisal of conscious and unconscious stimuli using the method of visual evoked potentials with P300 recording. Stimuli were words highlighted on the screen - indifferent and potentially significant for a patient (e.g. heroin). The stimulus related to the dominating motivation caused in patients the higher diffuse cortical activation on the unconscious level compared to non-targeted stimuli.