In Guillain-Barré syndrome (GBS), respiratory failure is a life-threatening complication, and its occurrence may be difficult to predict. We studied prospectively 10 patients with GBS by serial measurements of pulmonary function and arterial blood gases from the the time they were admitted to hospital. Five patients developed respiratory failure and had to be intubated, whereas the other five developed no ventilatory impairment. VC measurements were very useful in predicting respiratory failure several days before intubation. In patients who were eventually intubated, VC decreased during the 48 h preceding the occurrence of respiratory failure and intubation, which was required when VC was 15.2 +/- 3.7 ml/kg body weight (BW). In nonintubated patients, VC was stable and greater than 40 ml/kg BW. In addition, VC measurements allowed us to determine the beginning of the weaning procedure (no weaning trial could be performed successfully when VC was less than 7 ml/kg BW), to rationally follow its course, and to choose the time for extubation, i.e., when VC was greater than 15 ml/kg BW.