The use of low-dose L-deprenyl, a selective MAO-B inhibitor, in Alzheimer's disease patients has been associated previously with improvements in agitation and episodic learning and memory. Behavioral, cognitive, and regional electroencephalogram (EEG) measures were obtained in a 4-week open pilot study of 14 patients with probable Alzheimer's disease by NINCDS criteria who were administered 10 mg L-deprenyl per day. L-Deprenyl administration was associated with significant improvements on the agitation and depression factors of the Brief Psychiatric Rating Scale, the Cornell Scale for Depression in Dementia, and spouses' blind ratings. Recall improved on the Buschke Selective Reminding Task, but intrusions also tended to increase; verbal fluency decreased. Absolute EEG delta measures were selectively suppressed in the right frontal region. The pattern of changes suggests that L-deprenyl may be associated with improvement in behavioral and cognitive performance, in part through a mild behavioral disinhibiting effect.