We followed eight patients with Duchenne-type muscular dystrophy for an average of 39 months after initiation of noninvasive intermittent ventilatory assistance using body ventilators. After one to three months of nocturnal use averaging 8 h, mean daytime PaCO2 fell from 63 +/- 2 to 45 +/- 3 mm Hg. At late follow-up, PaCO2 remained stable at 47 +/- 4 mm Hg, but vital capacity fell 33 percent compared with the initial value and the average duration of ventilator use had increased to 18 +/- 2 h daily. Three patients died and five survived; two continued using negative pressure ventilators and three had tracheostomies placed for administration of positive pressure ventilation. We conclude that noninvasive intermittent ventilatory assistance effectively reverses hypoventilation and symptoms in patients with late-stage Duchenne muscular dystrophy, but pulmonary function continues to deteriorate necessitating longer periods of ventilation, and often tracheostomy, within a few years.