Interleukin-1 (IL-1) plays an important role in the pathogenesis of Graves' ophthalmopathy (GO). Impaired antagonism of the proinflammatory cytokine IL-1 by the naturally occurring IL-1 receptor antagonist (IL-1RA) has been implicated in the initiation and perpetuation of various autoimmune diseases and may play a role in the evolution of GO. Cigarette smoking appears to adversely affect the course of GO. We have evaluated the course of IL-1 alpha, IL-1 beta, and soluble IL-1RA (sIL-1RA) serum levels in smokers and nonsmokers with GO undergoing orbital radiotherapy (OR). We prospectively studied the eye status of 27 randomly selected patients (mean age 47.3 +/- 11.0 yr; 20 females; 18 smokers) with active, moderately severe GO before and 3 and 6 months following OR, respectively. None had received any previous treatment for GO, and all patients were kept euthyroid on carbimazole. Serum concentrations of IL-1 alpha, IL-1 beta, and sIL-1RA were measured using highly sensitive enzyme linked immunosorbent assay systems. Baseline sIL-1RA levels were negatively correlated with the number of cigarettes smoked before and following OR (P < 0.0001). Patients with no or minor therapeutic response to OR (n = 8), all of whom were smokers, revealed mean baseline sIL-1RA levels of 114 +/- 85 pg/mL, which increased to 172 +/- 103 pg/mL at 3 months and 149 +/- 96 pg/mL at 6 months after initiation of OR, respectively. By contrast, patients with a good clinical response (n = 19, 9 nonsmokers), revealed significantly higher baseline sIL-1RA levels at 294 +/- 148 pg/mL (P = 0.004), which increased to 845 +/- 668 pg/mL at 3 months (P = 0.01) and 634 +/- 337 pg/mL at 6 months (P < 0.001), respectively, following initiation of OR. Serum concentrations of IL-1 alpha IL-1 beta were below 3.9 pg/mL in all patients with GO who were studied, and were not correlated with gender, age, smoking status, clinical course, or outcome. Low baseline levels and impaired surge of sIL-1RA serum levels following OR were strongly correlated with smoking status and a less favorable therapeutic outcome in patients with active, moderately severe GO. Measurement of sIL-1RA may contribute to predict the therapeutic response to OR in patients with active, moderately severe GO. Strategies designed to raise local or systemic concentrations of sIL-1RA may be of benefit to patients with GO.