Oral occlusion pressure, a neuro-muscular index of the activity of the respiratory centers, was measured in 2 groups of children: one of 43 "healthy" children, in order to establish a predictive equation according to age (Y = 1.23 + 8.30 X A-1) and another of children presenting with respiratory failure, either due to an impairment of the thoracic cavity (10 dorsal scoliosis) or to an impairment of the respiratory muscles (29 children with muscular dystrophy or spinal muscular atrophy). The occlusion pressure increases with the degree of the ventilation deficiency in children with scoliosis. It remains paradoxically normal in children with neuro-muscular disease, irrespective of the ventilation deficiency. In the latter, the respiratory centers activity being considered as normal, this situation would indicate their muscular incapacity to correctly express this activity. It would show a severe muscular deficiency with a high risk of occurrence of respiratory distress accidents.