Five benzodiazepine drugs (diazepam, flunitrazepam, flurazepam HCl, nitrazepam and trazolam) were evaluated separately in 15 sleep laboratory studies with human subjects. Rebound insomnia, a worsening of sleep compared with baseline, occurred following withdrawal of triazolam, nitrazepam and flunitrazepam after they were given in only single, nightly doses for short periods. The rebound insomnia was attributed to the short and intermediate half-lives of these drugs. Diazepam and flurazepam, which have longer half-lives, did not cause rebound insomnia on withdrawal. Rebound insomnia may play a role in the development of hypnotic drug dependence with shorter-acting benzodiazepine drugs.