['Disturbed sleep is observed in association with acute and chronic pain, and some data suggest that disturbed and shortened sleep enhances pain. We report the first data showing, in healthy, pain-free, individuals, that modest reductions of sleep time and specific loss of rapid eye movement (REM) sleep produces hyperalgesia the following morning.', 'Two repeated-measures design protocols were conducted: (1) a sleep-loss protocol with 8 hours time-in-bed, 4 hours time-in-bed, and 0 hours time-in-bed conditions and (2) a REM sleep-loss protocol with 8 hours time-in-bed, 2 hours time-in-bed, REM deprivation, and non-REM yoked-control conditions.', 'The studies were conducted in an academic hospital sleep laboratory.', 'Healthy pain-free normal sleepers, 7 in the sleep-loss protocol and 6 in the REM sleep-loss protocol, participated.', 'Finger-withdrawal latency to a radiant heat stimulus tested at 10:30 AM and 2:30 PM and the Multiple Sleep Latency Test conducted at 10:00 AM, noon, 2:00 PM, and 4:00 PM were measured.', 'Finger-withdrawal latency was shortened by 25% after 4 hours of time in bed the previous night relative to 8 hours of time in bed (p < .05), and REM sleep deprivation relative to a non-REM yoked-control sleep-interruption condition shortened finger-withdrawal latency by 32% (p < .02).'] Are sleep loss and REM sleep loss hyperalgesic?