Growing male rats were allowed to have food from two dishes containing isocaloric, isoprotein 15% or 70% carbohydrate diet for 4, 8, 12 or 24 hours a day at the beginning of the dark period. Four hours of feeding were not enough to grow though the first 4 hours of intake were significantly higher than other periods. 4-hour and 8-hour feeding groups consumed significantly less carbohydrate calorie than 12-hour and ad libitum feeding groups, which hence, showed lower ratio of carbohydrate to protein in the total food consumed. The fasting brain tryptophan and serotonin levels among groups were not significantly different. It appears therefore that the manipulation of the feeding period could be valuable in suppression of carbohydrate appetitie, especially carbohydrate carving.