Eleven patients with inoperable brain tumours were treated with high doses of corticosteroids (methylprednisolone 200-2000 mg/day) for up to 151 days (mean 55 days). Neurological improvement occurred in eight patients on high doses after deterioration on concentional doses (methylprednisolone 80-120 mg/day). In two patients steroids could be completely discontinued for several months. Serious adverse effects included sepsis in three patients and myopathy in tow. All three patients with sepsis also received chemotherapy. There were no deaths that could be attributed to steroids. The most likely effect of high dosage steroids is reduction of cerebral oedema. It is conceivable that in some instances high dose steroids may also result in tumour inhibition or oncolysis or both.