Freeze-fracture studies were conducted in erythrocyte plasma membrane from 8 patients with Duchenne muscular dystrophy (DMD), 8 age-matched controls, 3 adult controls, 10 patients with myotonic muscular dystrophy, and 26 other neuromuscular disease controls. There was marked depletion of intramembranous particles in Duchenne dystrophy, whereas intramembranous particle density counts in other neuromuscular diseases were within normal limits. Therefore, the internal molecular architecture of the erythrocyte membrane is abnormal in Duchenne dystrophy, supporting the concept that a membrane defect involving multiple tissues is present in this disorder.