Summary The aim of the study was to investigate the recuperative value of brief and ultra-brief naps following nocturnal sleep restriction. Sixteen young adult healthy sleepers participated in a repeated measures design comprising four experimental conditions: no nap, 30-s nap, 90-s nap and 10-min nap. On the evening preceding each laboratory session, participants limited their nocturnal sleep to between 24:00 and 05:00 h. Measures of subjective alertness, objective alertness, fatigue, vigour and cognitive performance were taken before the nap and at several intervals postnap. Consistent with our previous study (Tietzel and Lack 2001), the 10-min nap resulted in significantly improved alertness and cognitive performance relative to a no-nap control. There were no measurable improvements for the 30- and 90-s nap conditions relative to no nap, which suggests that the mechanism underlying the benefits of brief naps does not appear to be the onset of stage 1 sleep. Further research is required to investigate whether the benefits of brief naps are because of the onset of stage 2 or delta wave sleep, or a specific duration of sleep between 90 s and 10 min.