OBJECTIVE: The primary objectives of this study were to evaluate the effects of initial and continued administration of buspirone on sleep induction and maintenance and sleep stage parameters, to determine the presence or absence of any drug-induced side effects, and to ascertain the presence or absence of sleep disturbances following abrupt withdrawal of the drug. METHOD: Six insomniac subjects who had chronic complaints of difficulty falling asleep and/or staying asleep and who were in good physical health, were not suffering from any major mental disorders, and had not used any medication for at least the last month participated in a 16-night sleep laboratory protocol. The protocol consisted of 4 placebo-baseline nights, 7 nights on which buspirone, 10 mg at bedtime, was administered, and 5 placebo-withdrawal nights. RESULTS: Wake time after sleep onset increased moderately during the first 3 nights of drug administration (there was a marked and significant increase on the first night) and increased by lesser degrees with continued drug administration. Overall, reports of side effects were infrequent. Following drug termination, there was a delayed and mild increase in sleep difficulty above baseline. CONCLUSIONS: These data not only confirm that buspirone lacks sedative effects but also suggest that the drug may have stimulant properties. Further, these findings suggest that buspirone has limited usefulness in anxious patients with concomitant sleep difficulties.