Two-hour, highly-selective, rest-period, rapid-eye-movement (REM)-sleep deprivation (RD) was performed on rats to characterize the time-course of the homeostatic response to REM-sleep loss. RD caused a dramatic and progressive increase in the frequency of attempts to enter REM sleep, suppressed non-REM sleep EEG delta power, and (in late rest period trials) was followed by a rebound increase in REM-sleep expression.