Carbohydrate homeostasis was evaluated in nine patients with Duchenne muscular dystrophy (DMD), and in six age-matched normal boys. Mild carbohydrate intolerance was observed in the DMD patients during an oral glucose tolerance test. Only minor differences were observed between the DMD patients and the normal subjects during a 30-hour period of caloric deprivation. Despite obvious muscle wasting and significant hypoalaninemia, the DMD group was resistant to fasting hypoglycemia. Plasma glutamine concentrations were the same in both groups under all study conditions. Deuterium-labeled glucose and alanine flux studies documented normal glucose inflow and outflow rates and decreased alanine inflow and outflow rates in the DMD group. The 40 percent reduction in alanine turnover, however, was less than expected for a group of patients with an estimated 67 percent reduction in muscle mass. These observations suggest that there may be accelerated protein degradation in the muscles of DMD patients.