The effects of different methods of treatment of Graves' ophthalmopathy were evaluated in a series of 48 patients. Thirty-six patients were given combined treatment with orbital cobalt irradiation and systemic 6 alpha-methylprednisolone (methylprednisolone). Included in this group were 12 of 24 consecutive patients who were randomly assigned to either combined therapy or systemic methylprednisolone alone. The degree of ocular involvement and responses to treatment were evaluated by numerical scoring (ophthalmopathy index) and clinical assessment. Of the 36 patients treated by combined therapy, 12 (33%) showed excellent responses, 14 (39%) showed good responses, 9 (25%) showed slight responses, and 1 (3%) had no response. Treatment was more effective for soft tissue involvement, newly developed ophthalmoplegia, and optic neuropathy, while proptosis and longstanding ophthalmoplegia were less responsive. There was an inverse relationship between the duration of ophthalmopathy and the efficacy of treatment, more favorable results being observed when symptoms had been present for less than 2 yr. Treatment with systemic methylprednisolone alone was also effective, but, in general, responses were less satisfactory; 4 of the 12 patients of this group (33%) had good responses, 6 (50%) had slight responses, and 2 (17%) had no response. The results obtained in the 24 patients randomly assigned to combined therapy or steroid treatment alone were compared by evaluating changes in the ophthalmopathy index. Mean initial ophthalmopathy indices (6.4 vs. 6.2, respectively) showed no significant differences between the 2 groups, whereas the mean decrease in the group receiving combined therapy (4.8) was significantly greater (P less than 0.05) than that in the other group (3.2). In conclusion, the present study indicates that both orbital cobalt irradiation combined with systemic methylprednisolone treatment and systemic methylprednisolone therapy alone are valuable methods of treatment for Graves' ophthalmopathy, but the combined therapy proved to be more effective.