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Two cases have been studied by means of the usual method for eliciting CNV (S-1.5 OR 1 SEC-S-operant response) during and after the end of an episode of prolonged epileptic twilight state with almost continuous strictly unilateral temporal lobe discharge. From the clinical viewpoint in both cases the twilight state, lasting respectively about 12 and 48 hours, was characterized by a slightly clouded consciousness and moderate impairment of awareness and of psychic performances, at times associated with simple and complex psychomotor automatism and hallucinations. The EEG recorded an almost continous left temporal discharge of pseudorhythmic mixed slow waves and sharps. The third case had typical prolonged petit mal states with continuous spike-and-slow-wave activity, impaired intellectual and motor performances (very long reaction time etc.). In this patient for eliciting ERSPs, besides the standard method, we have used a paradigm in which S consisted of a colored slide, with various semantic contents, remaining visible for 5 seconds on a screen. At the trials of the standard paradigm during the epiliptic twilight state, all patients showed they had understood the signal to interrupt (S loud repetitive tone) in the shortest time possible and could clearly distinguish them from the S. The operant response was almost always made with sufficient precision and sometimes with fairly short reaction time, especially by the patients with temporal psychomotor status. During the episodes of prolonged clouded consciosness in all series of trials administered to the patients, no negative slow potential shifts were observed in the averaged EEG recordings obtained from F-T, F-T or F, FCZ and referred to to linked mastoids. On repetition of the examinations some time after the end of the epileptic twilight state, fairly normal ERSPs were obtained in all cases. Taking also into account the results of previous researches, these studies show that the temporal lobe and "centrencephalic" epileptic discharges, under certain conditions, may influence negatively the neurophysiological mechanisms which contribute to the information of complex contingent connections and which also underly the particular attentional, cognitive and sensorimotor functions involved in the inhibiting the appearance of ERSPs probably related to more specific perceptual and integrative functions. Some AA. maintain that negative slow potential shifts express the functional activity of the brain structures, particularly of determined cerebral cortex regions, involved not only in attentional, perceptual, cognitive and psychomotor functioning, but also in information processing (memory recording mechanism). Hence, the negative influence of prolonged temporal lobe or meso-diencephalic epileptic discharges on these structures may explain the almost complete amnesia that patients generally show at the termination of this kind of twilight state.