Abnormal sweet-food craving may occur in subjects with Alzheimer's disease. This behavior may be due to abnormalities in the brain serotonin system. Fenfluramine stimulates the brain serotonin neurosystem, producing an increase in systemic prolactin. Using the fenfluramine stimulation test, brain serotonin system response was evaluated in 12 subjects with probable Alzheimer's disease. The subjects' caregivers completed questionnaires concerning subject food preferences and behaviors. Alzheimer's disease subjects with sweet-food craving were found to have a significantly higher response to fenfluramine than non sweet-food craving subjects. This preliminary study is limited by small sample size. Allowing for assumptions concerning central nervous system regulatory processes, the data suggest a possible role for the serotonin system in sweet-food craving in Alzheimer's disease.