Fig. 1. The chemical structure of bcnzquinamide concentration of amines in the brain. I t was well tolerated in i.v. and i.m. injection (1% and 10% respectively) as well as orally. The chemical formula is shown in Fig. 1. In preliminary clinical evaluations (FELn~AN 1962, ItASHKES 1962, SHULKIN et al. 1962, SMITH 1962, DABBS and PATERSON 1963, SAINZ 1963) benzquinamide appeared as an effective and safe tranquilizer for the control of anxiety and hypermotility, and its antiemetic effect was verified. Toxic effects were not encountered, and little drowsiness occurred. The dosage ranged from 100 to 1400 mg/day, usually divided in four oral doses because of the short duration of action. Doses as large as 1000mg q.i.d. (4000 mg/day) have actually been given by one author without dangerous effects. This seemed to be a very promising new drug. A dose range from 100 to 400 mg/day has most commonly been chosen for neurotic cases. We considered it important to determine experimentally the effects of benzquinamide on psychological performance in man. I t seemed suitable to compare it both with placebo and with chlordiazepoxide ("Librium") one of the most widely used tranquilizers in a doubleblind study.