Recently it has been hypothesized that triglyceride-fatty acid (tg-fa) recycling may play a role in modulating fuel availability during exercise in healthy volunteers. To test the hypothesis that alteration of normal tg-fa cycle activity might be involved in impairment of metabolic homeostasis in exercising IDDM patients, lipid and glucose turnover and oxidation will be assessed by stable isotope techniques and indirect calorimetry at rest, during 30 min exercise at 40% and 80% of VO2max and the first 30 min of recovery.