This study examined whether exposure to bright light treatment would reduce agitated behavior in institutionalized elderly subjects. Six demented elderly subjects (mean age = 89.2 years) living in a skilled nursing facility were studied. Light (2500 lx) was administered for 2 hours in the morning for two 10-day periods. The Bliwise Agitation Behavior Rating Scale was used to rate agitated behavior once every 15 min between 16:00 h and 20:00 h during 3 days of baseline, the light treatment periods, and 5 days of posttreatment follow-up evaluation. The entire protocol was then repeated in an ABABA design. A planned comparison revealed a significant difference between light treatment days and nontreatment days, with less agitation being observed on treatment days. The study suggests the efficacy of the clinical use of bright light treatment to reduce agitation.