We have evaluated the efficacy of high-dose intravenous immunoglobulin treatment in Graves' ophthalmopathy, and have carried out a prospective randomized clinical trial, including a single-blind evaluation, whereby 14 patients were assigned to two different treatment groups: 7 patients were treated with intravenous immunoglobulin and orbital radiotherapy (Group 1) and 7 patients were given intravenous immunoglobulin alone (Group 2). The results of the intravenous immunoglobulin treatment were also compared with those obtained in a Historical Control Group (12 patients) treated with systemic methylprednisolone and orbital irradiation. Degree of ocular involvement and response to treatment were assessed by ophthalmopathy index. The mean initial and final ophthalmopathy index showed no significant difference among the three groups. Comparison between the mean initial and final ophthalmopathy index showed a statistically significant reduction (p less than 0.005) in all three groups, the observed changes being confirmed by orbital computerized tomography in Groups 1 and 2. Corticosteroid treatment was associated with major and minor side effects, while no important adverse reactions were observed during intravenous immunoglobulin treatment. Even considering our results as preliminary, we conclude that intravenous immunoglobulin treatment is effective and safe in improving Graves' ophthalmopathy.