Twelve, healthy young men (mean age 25.6 years) consumed either ethanol (0.75 g/kg producing a peak breath ethanol concentration, BEC, of 0.060% on average) or placebo at 0900-0930 hr after spending 8 hr time-in-bed (TIB) the previous night and once again after 7 or 8 consecutive nights of 10 hr TIB. Latency to sleep onset (on the Multiple Sleep Latency Test, a standard measure of daytime sleepiness/alertness) was tested at 1000, 1200, 1400 and 1600 hr and divided attention performance was assessed at 1100 hr. Ethanol reduced sleep latency and divided attention performance and the sleep extension improved both sleep latency and divided attention performance. Sleep extension attenuated the sedating effects of ethanol; sleep latency after extending sleep did not differ between placebo and ethanol. While the effects of ethanol on performance still were detectable after sleep extension, the level of performance was at the 8-hr TIB placebo level. BEC peak and decline (determined before each latency test) did not change with the sleep extension. Hence, reduced BECs do not account for the reduction in the disruptive effects of ethanol with sleep extension.