Summary:Twenty epileptic patients (10 male and 10 female) were polygraphically recorded during nocturnal sleep. Ten subjects, with a wide age range, were affected by focal lesional epilepsy, and 10 were children affected by benign epilepsy with rolandic spikes (BERS). In five cases a bihemispheric expression of the focal lesional bursts emerged occasionally during the night recordings. The behavior of interictal electroencephalographic (EEG) paroxysms were analyzed with respect to the two arousal states of non‐rapid‐eye‐movement (REM) sleep: (a) the cyclic alternating pattern (CAP), expressed by biphasic EEG periodic activities and related to long‐lasting fluctuations between greater (phase A) and lesser (phase B) arousal levels; and (b) the non‐CAP (NCAP), manifested by EEG stationarities that reflect a sustained relative stability of arousal. The CAP/NCAP modality affected the spiking activity and distribution of the focal lesional EEG paroxysms, which appeared enhanced during CAP and which were mostly collected in phase A. The even more powerful influence of CAP and especially phase A on the secondary bisynchronous bursts suggests a crucial integration among thalamocortical circuits, arousal modulation, and epileptic generalization mechanisms. Conversely, in the BERS recordings no significant differences emerged throughout CAP and NCAP. The intense activity of the rolandic foci induced by sleep as such could be explained on the basis of the greater dependence of these functional cortical EEG abnormalities on the degree of synchronization dur