Graves' disease was originally described as a syndrome consisting of tachycardia, exophthalmos and goiter (triad of Merseburg). The concept of Graves' disease gradually evolved to a set of three conditions (hyperthyroidism, infiltrative ophthalmopathy and diffuse goiter) which may occur independently or in various combinations. With the development of more sophisticated diagnostic techniques, evidence of eye involvement can be found in most if not in all patients with thyroidal Graves' disease, while the vast majority of patients with Graves' ophthalmopathy have or will develop thyroid disease. Specific immunoglobulins are involved in the pathogenesis of Merseburg's triad (TSI in Graves' thyrotoxicosis, TGI in diffuse goiter, and presumably Olg in Graves' ophthalmopathy). A genetically determined antigen-specific defect in T-suppressor lymphocytes seems responsible for the production of these forbidden clones of immunoglobulins. It may be concluded that the overlap in thyroidal and ocular expressions of Graves' disease increases with every advance in diagnostic techniques. Accordingly it is a question of semantics whether one wishes to call Graves' ophthalmopathy and thyroidal Graves' disease part of one disease entity, or to consider these as two separate disease entities.