The posterior vector of the lid protractor force was measured in 29 patients with Graves' eye disease (GED) and 70 normal subjects. Patients with GED had significantly lower mean lid protractor force generation than normal subjects, although GED patients with compressive optic neuropathy did not show this difference. There was a negative correlation between the posterior force vectors and the exophthalmometer reading in GED patients only. It is conjectured that these two factors are linked by orbital and lid inflammation. The inflammation that increases orbital bulk, and thus increases the exophthalmometer reading, may well cause atrophy in the orbicularis oculi muscles, decreasing its force generation.