To evaluate the efficacy of high-dose intravenous steroid pulse followed by oral steroids in the treatment of thyroid-associated ophthalmopathy, we performed clinical assessment and measurement of retroorbital muscle enlargement in 27 patients before and after the therapy, and followed them up longitudinally. The mean duration of follow up is (mean +/- SD) 29.8 +/- 23.8 months (range 4-92). Diplopia disappeared in 10 patients and ameliorated in 11 patients. The degree of proptosis decreased in 15 patients and the fall in visual acuity improved in a third of the patients. The total ophthalmopathy index (OI) decreased from 7.0 +/- 1.9 to 3.0 +/- 1.5. The extraocular muscle enlargement (EME), expressed as the maximal ratio of extraocular muscle thickness to the diameter of the optic nerve, decreased from 2.33 +/- 0.56 to 1.27 +/- 0.26. No major side effects were found in any patient. The improvement in the eye disease was found immediately after the pulse therapy, prior to the start of the following therapy by oral steroids and/or orbital irradiation. Both of OI and EME decreased with time after the therapy and did not get worse after withdrawing oral steroids. The efficacy of the therapy evaluated by degrees of improvement in OI and in EME was significantly greater in females than in males. Although there was a significant positive correlation between initial OI and EME values and initial TBII and TSAb activities, a significant correlation was seen only between the degrees of improvement in EME and changes in TBII activity due to the therapy. The duration of eye disease, thyroid status, treatment with anti-thyroid drug, smoking and experience of previous treatment did not affect the efficacy of the present therapy. We conclude that high-dose intravenous steroid pulse therapy is effective and safe for thyroid-associated ophthalmopathy.