The electrical seizure activity and trancelike state induced in the rhesus monkey by gammahydroxybutyrate (GHB) were abolished by dextroamphetamine. Dextroamphetamine blockade of this neurophysiologic effect was overcome with chlorpromazine, a dopamine receptor blocker. These results suggest that the electroencephalographic (EEG) and behavioral effects of GHB are related to effects on dopaminergic systems. Such a relationship, if substantiated by further studies, might indicate that anticonvulsant drugs used to treat petitma1 epilepsy have a dopaminergic mode of action.