Glucocorticoids are usually given for management of Graves' ophthalmopathy (GO), but they may cause side effects. By comparison, intravenous administration of immunoglobulins resulted in clinical improvement and decreased antibody titres in a large number of autoimmune diseases. Therefore, a randomized trial was done, in which 19 patients with active GO were treated with a 20-week course of oral prednisolone (P, starting dose 100 mg/day), and 21 received 1 g immunoglobulin/kg body weight for 2 consecutive days every 3 weeks. The immunoglobulin course was repeated six times. Before and at the end (20 weeks) of immunomodulating therapy, ophthalmological investigation and quantitative magnetic resonance (MR) imaging were performed. A successful outcome was observed in 12 (63%) P- and in 13 (62%) immunoglobulin-treated patients. Overall, there were no marked differences in degree of improvement between the two groups. Responders to treatment in both groups showed improvements in proptosis (median from 24.5 to 21.5 mm; P < 0.005), visual acuity (from 0.6 to 0.85; P < 0.001), intraocular pressure (from 25 to 20 mmHg; P < 0.0001), lid aperture (from 14 to 12 mm: P < 0.01) and a decrease in eye muscle area (inferior, from 44 to 33 mm2; medial, from 43 to 34 mm2; both P < 0.0005). Among the immunoglobulin-treated patients, there was a marked decrease of thyroid antibody titres. Side effects were more frequent and severe during P than during immunoglobulin therapy. Thus, with respect to the above mentioned objective parameters, P and immunoglobulin appeared to be equally effective in treatment of active GO.