Habitual sugar consumption and behavior following challenge by sugar and aspartame were studied in 30 preschool boys. The 18 subjects whose parents considered them sugar reactive had more disruptive behavior problems at baseline than the other 12 subjects. Habitual sugar consumption correlated only with duration of aggression against property in alleged responders. Double-blind crossover challenges with aspartame, saccharin, sucrose, and glucose produced no significant effect on aggression or observers' ratings of behavior. Lower actometer counts followed the trials of aspartame, but the difference was not apparent to observers. It is unlikely that sugar and aspartame are clinically significant causes of disruptive behavior.