In a retrospective analysis of 40 hospitalized patients with the Guillain-Barré syndrome (GBS), we related the use and outcome of assisted ventilation to specific quantitative details of the neurologic illness. Two patients had an unusually prolonged course: they were ventilated for 374 and 396 days before successful weaning. The other 38 patients were similar in most respects to those in previously reported series. Sixteen ventilated patients were hospitalized 56.6 +/- 10.6 (mean +/- S.E.M.) days, were ventilated 27.9 +/- 6.5 days, and had primarily pulmonary complications. There were 4 deaths during ventilation, and 9 of 13 survivors (69%) had a short-term excellent functional neurologic outcome. Attention to the neurologic details of the course of illness may spare some patients from tracheostomy. Twenty-two patients not requiring respirator support suffered distinctly less severe neuromuscular impairment with minimal cranial neuropathy, had no occurrence of pneumonia, and were discharged after 19.1 +/- 4.6 days. Eighty-one percent had an excellent functional outcome. The wide range of manifestations and severity of patients with GBS requires the attending physician to be flexible in dealing with each case and not make management decisions arbitrarily, by reference to a hypothetical "typical case."