Oxygen uptake during treadmill walking was measured in 8 scoliotic patients with idiopathic curves ranging from 25 to 60°. The patients were fitted with a Milwaukee brace and the test was repeated within 2 or 3 days to study the effect of the brace on energy expenditure, mechanical work, and ventilatory function. The total oxygen uptake was not systematically affected by wearing the brace. When the weight of the brace was included, the oxygen uptake/kg body weight decreased in most of the patients at low walking speed in spite of an increased lift work. The positive influence on energy expenditure was interpreted as a stabilizing effect of the brace on the spine. This effect was not consistent at moderate and high speeds of locomotion, where both a decrease and an increase in oxygen uptake/kg were observed. Heart rate increased significantly during walking at high speed with the brace, while a slight but significant reduction of the tidal volume was found during walking at low speed.