OBJECTIVE: The purpose of this study was to compare the effects of discontinuing treatment with intermediate- and long-acting benzodiazepines. METHOD: Fifty patients with panic disorder who had taken part in a double-blind treatment study and had responded to alprazolam, diazepam, or placebo for 8 months were asked to stop taking these medications gradually. RESULTS: After a relatively rapid dose reduction, the majority of patients relapsed. Rebound anxiety and withdrawal symptoms were identified in a substantial minority of patients. Those who were taking alprazolam showed earlier and more intense rebound anxiety and withdrawal symptoms than did the patients who received diazepam. Both the level of pretreatment anxiety and the drug the patient was taking predicted the level of anxiety when drug treatment was discontinued. CONCLUSIONS: The findings indicate that withdrawal phenomena commonly occur after patients stop taking benzodiazepines and that they are more frequent after discontinuation of treatment with shorter-acting drugs.