A previous study demonstrated the efficacy of the corticotropin-releasing hormone (CRH) receptor antagonist, α -helical CRH (9—41), in blocking the paradoxical sleep increase induced by stress. In the present study, this peptide was used to evaluate the involvement of the stress component of the sleep deprivation, in the paradoxical sleep rebound. Rats were subjected for 10 h to the classical water-tank sleep-deprivation technique and were given, every 2 h throughout the sleep deprivation period, intracerebroventricular injections of either 100 µg/5 µI of a-helical CRH (9—41) or vehicle alone. Continuous recordings showed that antagonist treatment decreased the PS rebound, but not the SWS rebound, following sleep deprivation. These findings suggest that, in the water-tank sleep deprivation method, stress, acting via CRH activation, is the main factor inducing the paradoxical sleep rebound.