Alternate-day corticosteroid therapy was compared with two daily corticosteroid regimens for the treatment of giant cell arteritis. In a prospective study 60 patients with this disease were randomly assigned to three treatment groups: group A, 15 mg of prednisone every 8 hours; group B, 45 mg of prednisone every morning; and group C, 90 mgof prednisone every other morning. After 1 month of treatment, the arteritis seemed to be completely suppressed in 18 patients in group A and 16 in group B but in only 6 in group C. In the 14 other patients in group C, the continuing symptoms were cyclic and developed during the day steroids were not given. By changing to a daily regimen, the arteritis was controlled in most patients in group C. Adverse reactions to prednisone were noted frequently in groups A and B but rarely in group C.