Previous studies have suggested that accelerated protein degradation or a reduced rate of protein synthesis is the process responsible for muscle wasting in Duchenne dystrophy. Skeletal muscle biopsies were obtained from 4 Duchenne dystrophy and 6 normal male orthopaedic control patients. Muscle cultures were established from dissociated single cells and protein metabolism was studied in mixed, confluent, post-fusion cultures. The rate of total protein synthesis was significantly greater in Duchenne cultures, while the degradation rate of long half-life protein was not significantly different in Duchenne dystrophy and control cultures. Monoclonal cultures from 1 Duchenne and 1 control biopsy demonstrated considerable variation in protein synthesis and degradation rates and creatine kinase activity between clones from each biopsy. This suggests that individual myoblasts differ significantly in growth and myogenic potential.