The present study investigated the effects of the benzodiazepine receptor antagonist RO 15-1788 on the ability to resist sleep after 1 night of sleep deprivation. Repeated administrations of RO 15-1788 to 6 subjects significantly decreased their ability to resist sleep in comparison with repeated administrations of 100 mg of vitamin C, and with a nontreatment condition. Most of the hypnotic effect occurred 80–100 min after drug ingestion. RO 15-1788 also significantly enhanced sleep stage 2 spindles activity. These results demonstrate that at certain dosages RO 15-1788 has agonist-like effect