A group of 19 middle aged patients suffering from primary insomnia according to the DSM-III-R were treated in a single-blind study with trimipramine, a sedating antidepressant. A total of 15 patients completed the study protocol and were evaluated. The present pilot study aimed at investigating the sleep-inducing properties of trimipramine, and at clarifying the question of whether short- or long-term rebound insomnia occurs after discontinuation of this drug. At four measurement points, i.e. under baseline conditions, under treatment and 4 and 14 days after drug discontinuation, sleep was recorded with an ambulatory-electroencephalogram (EEG) monitoring device in the patient's home environment. Simultaneously, psychometric tests were applied to measure withdrawal symptoms, subjective sleep quality and well-being during daytime. Trimipramine at a mean dose of 166 +/- 48 mg led to a significant increase in sleep efficiency, total sleep time, and stage 2% sleep-period time (SPT), whereas a significant decrease in wake time and stage 1% SPT was noted. Insomniac patients reported an improvement in subjectively perceived sleep quality following trimipramine. Additionally, an improvement in well-being during the daytime occurred. Negative side effects were limited to dry mouth due to the anticholinergic properties of the drug. Discontinuation of trimipramine did not provoke either short- or long-term rebound insomnia in objective and subjective sleep measurements considering mean values of the whole sample, although a subgroup of patients did display total sleep times below baseline values during short- and long-term withdrawal, but generally without a concomitant worsening of sleep quality according to the sleep questionnaire.