Ten healthy volunteers were injected i.v. with 5 mg Ro 15-1788, a specific benzodiazepine antagonist, or placebo in a double-blind randomised design. In the EEG, Ro 15-1788 led--with some topographical variations--to a diminution of theta and alpha power, an increase of alpha mean frequency and a decrease of delta mean frequency. In auditory evoked potentials, the N1P2 and P2N2 amplitudes decreased. The electrophysiological changes induced by Ro 15-1788 are consistent with a central stimulant action. Ro 15-1788 induced some slight behavioural and subjective changes.