Effects of skipping breakfast on speed and accuracy of response in a number of problem solving tasks were assessed in 9- to 11-yr-old, well-nourished children. The conceptual framework for this study was derived from an experimental model of the effects of mild environmental stress, e.g., noise, on human performance. Plasma glucose, beta-hydroxybutyrate, lactate, and free fatty acids were used as indicators of the induced metabolic stress, and the extent of their association with the behavioral measures was determined. Fasting had an adverse effect on the accuracy of responses in problem solving, but it had a beneficial effect on immediate recall in short-term memory. Both effects are explained by a heightened arousal level associated with the brief experimental fast.