Breakdown of glycogen in liver and muscle and of triacylglycerol in adipose tissue is usually regarded as part of the early neuroendocrine response to trauma. This review discusses the extent to which such body fuel mobilization actually occurs after injury in man and experimental animals. It describes the effects of injury on the activity of the neuroendocrinesystems capable of stimulating glycogen and triacylglycerol brakdown and discusses which ones are likely to be responsible for the changes observed. It describes the resulting changes in concentration of glucose, lactate, free fatty acids and ketone bodies and examines some of their implications, e.g. for the maintenance of blood volume.