The benzodiazepine receptor antagonist 3-hydroxymethyl-beta-carboline, which blocks several of the pharmacological actions of benzodiazepines, induces a dose-dependent increase in sleep latency in the rat. Furthermore, at a low dose that by itself does not affect sleep, 3-hydroxymethyl-beta-carboline blocks sleep induction by a large dose of flurazepam. The benzodiazepine receptor may play a role in both the physiological regulation and pharmacological induction of sleep.