We determined serum levels of laminin in 23 patients with Graves' disease (GD) and in 24 patients with toxic nodular goiter (TNG). Elevated levels of soluble laminin were observed in patients with GD prior to treatment (median concentration 1376 ng mL-1 [range 712-2402]), compared to patients with TNG (median 442 ng mL-1 [284-891]), and normal controls (median 492 ng mL-1 [range 235-675], n = 26), respectively. In GD patients serum laminin levels decreased during thiamazole treatment and normalized within 8 weeks of therapy. There was no correlation between serum laminin levels and serum levels of thyroid hormones and/or auto-antibodies, respectively. Whether serum laminin is a marker for alterations of extracellular matrix during GD and release of basement membrane components in the circulation and/or reflects an impaired clearance remains to be elucidated.