Fatigue is a common symptom of multiple sclerosis (MS) that is without an effective treatment. A double-blind, controlled study of fatigue treatment was conducted to evaluate the efficacy of amantadine hydrochloride in treating MS-associated fatigue. Since fatigue cannot be characterized by a single symptom or behavior, a variety of neuropsychological, behavioral, and self-report measures were used to monitor changes across different systems. According to patients' daily diary ratings, amantadine produced small but statistically significant improvements in fatigue across four of seven dimensions (overall energy level, concentration, problem solving, and sense of well-being). In addition, patients with MS who were taking amantadine performed slightly better on the Stroop Interference Test, an attentional measure of freedom from distracting information. Although retrospective reports by patients with MS did not confirm the degree of improvement recorded on a daily basis, the study's results suggested that amantadine may offer modest benefits in alleviating the day-to-day subjective experience of fatigue.