Serum concentrations of soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble E-selectin (sE-selectin), soluble P-selectin, and soluble L-selectin (sL-selectin), tumor necrosis factor-alpha, and interleukin-6 were measured in patients with Graves' disease (GD) (n = 33), in patients with toxic nodular goiter (n = 34), and in a group of healthy controls (n = 36). The serum levels of sICAM-1, sVCAM-1, sE-selectin, and sL-selectin were markedly elevated in patients with GD and in patients with toxic nodular goiter before treatment with methimazole (P < 0.05 for all). After 8 weeks of therapy, serum concentrations of sVCAM-1 and sE-selectin normalized, whereas serum levels of sL-selectin and sICAM-1 remained elevated. Hormone concentrations normalized after 2 weeks, clearly preceding falling levels of circulating adhesion molecules. Serum concentrations of soluble P-selectin, TNF-alpha, and interleukin-6 did not differ among patients with GD and toxic nodular goiter and healthy subjects. Serum levels of sVCAM-1 and sICAM-1 correlated with the serum concentrations of TSH receptor antibodies (n = 33; r = 0.921 and r = 0.792, respectively) and thyroid peroxidase antibodies (n = 33; r = 0.682 and r = 0.761, respectively) but not thyroglobulin antibodies. However, no correlation between serum levels of sE-selectin, sL-selectin, and soluble P-selectin or cytokines and serum levels of thyroid peroxidase antibodies, TSH receptor antibodies, or thyroglobulin antibodies, respectively, was found. In addition, no correlation between serum levels of adhesion molecules or cytokines and thyroid hormones was seen. We conclude that both the action of thyroid hormones and the autoimmune process in GD may contribute to elevated levels of soluble adhesion molecules.