Precise measurements of treatment response are a prerequisite for correct interpretation of therapeutic benefit. In the field of Graves' ophthalmopathy we have relied for too long on methods of measurement that are poorly reproducible, subjective, and that often rely on indices derived from aggregated measurements and subjective impressions. In consequence, our conclusions about the benefits of particular therapies are frequently controversial. Until the pathogenic agent of Graves' ophthalmopathy has been identified and is measurable, we are forced to limit our observations to the consequences of the action of that agent. Two critically important consequences are swelling of the retrobulbar muscles and connective tissue and shortening of the extraocular muscle range of contraction. From these primary events all the clinical features of Graves' ophthalmopathy are derived. Effective treatment of Graves' eye disease will affect at least one of five relevant measurements. These are: lid fissure width, range of extraocular motion, diplopia fields, and volume of retrobulbar muscle and connective tissue. These measurements, selected to correspond to the claims of the particular therapy under study, are recommended as the indicators of choice in clinical trials.