Twelve normal subjects were tested on a number of measures both before and 1,3 and 5 h after 10 mg diazepam, 100 and 200 mg tofisopam and a placebo. The measures included self-ratings of mood, bodily symptoms, hostility and sleep, the electroencephalogram (EEG), reaction time, tapping, digit symbol substitution, the symbol copying test, and plasma levels. Diazepam showed a clear profile of action, producing EEG changes, pronounced sedation and psychological impairment. The last two effects were maximal at 1 h and had worn off by 5 h. The EEG was recorded at 3 h only. Tofisopam in no way resembled diazepam. It produced no changes on the EEG or psychological tests and a very mild stimulant effect was apparent on the ratings. While diazepam was easily detectable in the blood, tofisopam did not bind to benzodiazepine receptors.