To test the efficacy of a specially-formulated, carbohydrate-rich beverage (one known to increase the serum ratio of tryptophan to other large neutral amino acids) on the mood, cognitive, and appetitive disturbances of premenstrual syndrome (PMS). Twenty-four women with confirmed PMS were enrolled in a double-blind, crossover study to test the efficacy of the specially-formulated beverage compared with two other isocaloric products on PMS symptoms. The study was conducted over three menstrual cycles preceded by a 1-month placebo run-in. Patients were tested at home or work using an interactive computer-telephone system. Standardized measurements of mood, cognitive performance, and food cravings were made before and 30, 90, and 180 minutes after consumption of active and placebo beverages during the late luteal phase of the menstrual cycle. The experimental carbohydrate intervention significantly decreased self-reported depression, anger, confusion, and carbohydrate craving 90-180 minutes after intake. Memory word recognition was also improved significantly compared with scores obtained during the placebo run-in month (P < .05). The isocaloric placebo interventions had no significant effect on any of these measures. The results suggest that the psychological and appetitive symptoms of PMS can be relieved after consuming a specially-formulated, carbohydrate-rich beverage known to increase serum tryptophan levels.