Bromocriptine mesylate (7.5 mg/kg, i.p.) and dihydroergotoxine mesylate (DHET); 3 mg/kg, i.p.) were administered 4 times at 9-hour intervals within a 27-hour period to rats polygraphically recorded for 84 h. Administration of bromocriptine resulted in increased wakefulness and reduced slow-wave sleep (SWS) and rapid eye movement sleep (REM) during the 0- to 36-hour period. Reduction of SWS or REM during this time period was not followed by a rebound of SWS or REM during the next 36- to 84-hour period. In addition, there was a significant reduction of SWS during the entire 0- to 84-hour period. Administration of DHET to rats did not significantly affect sleep although there was a tendency for wakefulness to increase and for SWS and REM to decrease. It appears that the effects of repeated administration of the two ergot compounds on the sleep-wakefulness cycle in rats may be indicative of the drugs' role in fulfillment of sleep 'need'.