Clonazepam 0.5 mg was evaluated in a sleep laboratory study of 6 insomniac patients. The 16-night protocol consisted of 4 placebo-baseline nights, 7 nights of drug administration and 5 placebo-withdrawal nights. Clonazepam produced a significant decrease in total wake time initially (nights 5-7), as well as with continued administration (nights 9-11). With later but not immediate withdrawal, significant rebound insomnia occurred, on the 3rd withdrawal night, both wake time after sleep onset and total wake time increased markedly, with the latter significantly increased. These findings are discussed in light of clonazepam's increasing use for panic disorder; specifically, due to its maintained efficacy, it has the advantage of avoiding interdose rebound anxiety which is frequently reported with use of alprazolam.