The effects of systemic injections of beta-carboline-3-carboxylate-t-butyl ester (beta-CCtB) were investigated with regard to normally occurring sleep and several measures of benzodiazepine receptor occupancy in rats. A dose of 30 mg/kg of beta-CCtB was found to have a long time-course of action as measured by an in vivo assay for benzodiazepine binding, with an 84% depletion of [3H]diazepam binding at one hour after the intraperitoneal injection. This dose of beta-CCtB was shown to delay sleep onset, decrease non-REM and total sleep in the first two hours after the injection, and to delay the appearance of REM sleep after the sleep onset. The dose- and time-dependence of the effects on sleep approximated the dose- and time-dependence of inhibitory effects of an IP injection of beta-CCtB on in vitro measures of benzodiazepine receptor affinity and number.