Glucocorticoid in high dose has known to reduce vascular sensitivity to various vasoconstrictive stimuli. It inhibits phospholipase to reduce production of prostaglandins. It stabilizes the cell membrane and prevents cerebral edema. All these pharmacological effects indicate possible usefulness of this drug for the treatment of cerebral ischemia due to vasospasm. Based on these theoretical backgrounds a multi-center controlled double blind clinical study was carried out. The patient who showed manifestations of delayed cerebral ischemia due to vasospasm were selected for this study. As soon as the clinical manifestation appeared, the patient was given either 3 grams of hydrocortisone intravenously in a 60 ml solution or the placebo. The administration was repeated 6 times with interval of 12 hours. The patients were allowed to be treated according to the independent protocol of each institute except for the maximum daily use of glucocorticoid. The effect of the therapy was evaluated at 4th, 7th day and 1 month after the initiation. The study involved 52 institutes and a total of 140 patients, seventy-one patients who received hydrocortisone (group A) and 69 patients who received placebo (group P) was analysed. There were no significant differences in background data between both groups. In patients with grade I, II or III on admission, the favorable effects of hydrocortisone were demonstrated on changes in neurological findings. In group A, there were significantly more cases of improvement at 4th day for orientation about place and person. At 1 month or on discharge group A showed significant improvement almost in every aspect of neurological findings including mental, speech and motor functions.(ABSTRACT TRUNCATED AT 250 WORDS)