Dihydroergotoxine mesylate (DHET; active substance of Hydergine®) and dihydro- β-ergosine altered the sleep-wakefulness cycle of the rat by increasing wakefulness and decreasing slow wave and rapid eye movement sleep. In addition, power spectrum analysis indicated that, in comparison with placebo, DHET increased total power. Dihydro-Ø-ergosine increased relative power in the θ- (4–8 Hz) and in the fast β- (30–40 Hz) bands of the electrocorticogram. The alterations in the sleep-wakefulness cycle and in the distribution of power in the rat electrocorticogram are discussed as possible indices of changes in alertness and at