A 10-week study was conducted in which all food was provided for the families of 24 hyperactive preschool-aged boys whose parents reported the existence of sleep problems or physical signs and symptoms. A within-subject crossover design was used, and the study was divided into three periods: a baseline period of 3 weeks, a placebo-control period of 3 weeks, and an experimental diet period of 4 weeks. The experimental diet was broader than those studied previously in that it eliminated not only artificial colors and flavors but also chocolate, monosodium glutamate, preservatives, caffeine, and any substance that families reported might affect their specific child. The diet was also low in simple sugars, and it was dairy free if the family reported a history of possible problems with cow's milk. According to the parental report, more than half of the subjects exhibited a reliable improvement in behavior and negligible placebo effects. In addition, several nonbehavioral variables tended to improve while the children received the experimental diet, particularly halitosis, night awakenings, and latency to sleep onset.