We investigated the lymphocyte characteristics of 77 Graves' disease patients with and without infiltrative ophthalmopathy. Thirteen patients with infiltrative ophthalmopathy without prior antithyroid therapy and 20 euthyroid patients with progressive ophthalmopathy demonstrated decreased percentages of active and total erythrocyte rosette-forming lymphocytes compared to thyrotoxic patients without eye disease and to a control population (p less than 0.001). There was no significant difference in rosette-forming cells between untreated thyrotoxic and treated euthyroid patients with ophthalmopathy. No lymphocytotoxic antibodies or rosette inhibitory factor was present in the sera of patients with infiltrative ophthalmopathy. Untreated and treated patients with lid retraction and mild proptosis without extraocular muscle disease had decreased active rosette-forming cells (p less than 0.001) but normal total rosette-forming cells. Five patients with infiltrative ophthalmopathy who failed to improve with systemic corticosteroids demonstrated elevated active but normal total rosette-forming cells. Differences in rosette formation between ophthalmic and nonophthalmic Graves' disease may represent an associated cell-mediated abnormality that may explain why control of the thyrotoxic state need not correlate with the ophthalmic manifestations of the disorder.