Early morning insomnia, a significant increase in wakefulness during the final hours of drug nights, occurred after 1 or 2 weeks of nightly administration of benzodiazepine hypnotics with short elimination half-lives, when tolerance had begun to develop. Early morning insomnia may be a variant of rebound insomnia and therefore specific to benzodiazepines, or it may occur with any rapidly eliminated sedative-hypnotic agent.