It is well established that the side-effects of corticosteroid treatment can be reduced by administering the steroid on alternate days. Twenty-seven patients with giant cell arteritis were given daily treatment initially, followed by a gradual transition to alternate-day treatment. It was possible to maintain 18 (67%) of 27 patients on this regimen. In 9 (33%) the regimen was abandoned because of clinical symptoms on the "day off". These patient, however, could be maintained with a single morning dose of the corticosteroid. Morning plasma cortisol levels on the treatment day were normal in all patients treated with 20 mg prednisolone or less every other day.