1. The patient population consisting of fifteen patients was divided into three groups, namely: diazepam group, phenobarbital group and placebo group. After three weeks the medicated groups were switched to placebo for a week and the placebo group was given phenobarbital. 2. The parameters to be assessed once a week comprised frequency-analyzed EEG recordings, performance in two attention tests and subjectively estimated mood modalities. 3. The EEG analysis suggested that EEG patterns: a) were drug-dependent, with a differential distribution for each drug of the four frequency bands analyzed; b) showed no change during the three-week treatment period; c) changed on cessation of medication or on switch from placebo to active medication; d) were task-dependent and changed in a systematic way with the level of activation (stress, vigilance or relaxation). 4. The results would allow a better understanding of the clinical course, the choice of therapeutic measures and of the underlying mechanisms of action.