The efficacy of steroids in the treatment of acute idiopathic polyneuritis (Guillain-Barré syndrome) continues to be uncertain. Since 1965, 38 patients with idiopathic polyneuritis have been seen at the University of Kentucky Medical Center, and 16 of them were entered in a prospective double-blind study designed to assess the effectiveness of steroid therapy. Seriously ill patients were excluded from the study and most of them received steroids. In both the double-blind group and the entire group of patients, the time from onset of illness to recovery was significantly less in patients treated with steroids, although steroids did not alter the initial severity of illness or the duration of hospitalization.