The abnormal metabolic responses to exercise in insulin-dependent diabetes are in great part related to abnormal circulating plasma insulin concentrations. Exercising during relative insulin deprivation results in an increase in glycemia and ketosis. Exercise during insulin excess results in inhibition of hepatic glucose production and accelerated muscle glucose utilization and results in hypoglycemia. These responses can be significantly improved when insulin is administered more appropriately, as is the case with insulin infusion pumps. Self blood glucose monitoring before, during, and after exercise can provide important information that can be used to optimize the metabolic response to exercise in individual patients. A better understanding of the metabolic response to exercise in patients with diabetes will serve as the basis for developing specific recommendations to enable these individuals to have the freedom to take part in all forms of exercise with minimal restriction. However, the demonstration that exercise will have a long-term beneficial effect on the metabolic control of diabetes or prevent the development of the complications of diabetes remains to be established.