Ninety‐six patients with Duchenne muscular dystrophy (DMD) were randomized and placed either on placebo or oral leucine at a dose of 0.2 g per kg per day. Patients were evaluated using a protocol that measured muscle strength, joint contracture, functional grade and activity, and pulmonary function tests. After 1 month there was a transient but significant difference in the strength of the two groups, the treated group being stronger than the placebo group. At 6 months there was also a transient difference in joint contracture measurements. Analysis of the data showed that the difference between the groups for both these measurements could not be ascribed to a therapeutic effect of leucine but rather to an unexpected drop in the placebo group. This was recognized only because the slope of deterioration for these functions had been well documented during the natural history phase of the study. These results indicate that oral leucine failed to produce a therapeutic response over a 1‐year double‐blind, controlled trial.