Clonazepam (1 mg h.s.) and temazepam (30 mg h.s.) were studied in 10 patients diagnosed as having insomnia with nocturnal myoclonus. Each subject underwent two nocturnal polysomnographic recordings while drug-free, two during treatment with clonazepam, and two during treatment with temazepam. Treatment sessions were 7 days long, and recordings were done on nights 6 and 7 of the treatment sessions. A 14-day washout period separated the treatment sessions. The order of drugs used in the first and second treatment sessions was randomized. Objective and subjective sleep laboratory data showed that both drugs improved the sleep of patients with insomnia in association with nocturnal myoclonus. Neither drug significantly reduced the number of nocturnal myoclonic events. Sleep changes were consistent with those produced by sedative benzodiazepines in general. Thus, the data support clinical reports that clonazepam, a benzodiazepine marketed for the indication of seizure, is useful in improving sleep disturbances associated with nocturnal myoclonus. Temazepam, a benzodiazepine marketed for the indication of insomnia, was found to be a suitable alternative to clonazepam in the treatment of insomnia associated with nocturnal myoclonus. The present data and other studies suggest the need for a model that explains why leg movements and sleep disturbances may wax and wane independently.