Seven-hr sleep recordings were performed on rats following intraperitoneal injection of saline or one of four doses of ethanol (1.1, 1.5, 2.0 or 2.5 g/kg). Total minutes of REM sleep and percentage REM sleep were decreased in a dose-dependent manner. Percentage nonREM sleep increased with progressively higher doses. The decrease in REM sleep appeared to be related to a decrease in the number of REM sleep episodes and an increase in the length of the REM-nonREM cycle. Other variables such as mean length of REM sleep episodes and REM sleep efficiency were unchanged. An analysis of the first and second 3.5 hr of the recording showed that ethanol continued to have marked effects on REM and nonREM sleep during the second 3.5 hr, when blood levels were declining. Ethanol produced decreases in sleep latency, but total sleep time was unchanged.