We have previously reported that microinjections of the benzodiazepine hypnotic triazolam into the medial preoptic area (MPA) of the hypothalamus enhance sleep in rats. The present study further characterizes this effect, by examining its anatomical specificity, determining whether it is mediated by interaction with central benzodiazepine receptors, and assessing whether sleep induction is associated with changes in core temperature. It was found that microinjections of 0.25 and 0.5 micrograms triazolam into two nearby structures, the lateral preoptic area and diagonal band of Broca, failed to alter sleep. Total sleep time was enhanced by microinjection of triazolam into the MPA, and this effect was blocked by co-administration of the benzodiazepine receptor blocker RO 15-1788. Sleep enhancement by triazolam was not associated with significant alterations in core body temperature. These observations continue to suggest that the MPA may be a site which mediates the hypnotic effect of triazolam, and add to the growing body of data emphasizing the importance of hypothalamic function in the regulation of sleep and waking.