1 This study was performed because dose-related effects of heroin on human sleep had not been described previously, and to discover if heroin produces a morphine-like insomnia. 2 After three adaptation nights, the sleep of seven male nondependent opiate addicts was studied following i.m. doses of heroin (3, 6, 12 mg/70 kg), morphine (10, 20 mg/70 kg) or placebo at weekly intervals in a randomized double-blind crossover design. 3 Heroin produces a dose-related increase in wakefulness, drowsiness episodes, muscle tension, and shifts in sleep-waking states.I 4 Heroin produces a dose-related decrease in total sleep, sleep efficiency, delta sleep and REM sleep (REMS). 5 Heroin is about twice as potent as morphine in producing this type of insomnia. 6 'Morphine insomnia' appears to be a characteristic initial effect of several opioids, at least in nondependent opiate addicts, and might serve as a model insomnia for evaluation of hypnotics.