Localized scleroderma has been reported to be accompanied by abnormal immune reactions, including autoantibody production and lymphocyte activation. Lymphocyte activation can be quantitatively detected by measuring soluble interleukin-2 receptor (sIL-2R) in serum samples. In this study, serum sIL-2R levels were assayed by a sensitive enzyme-linked immunosorbent assay, in 48 patients with localized scleroderma, in 20 with systemic sclerosis (SSc) and in 20 healthy controls. Serum levels of sIL-2R were significantly higher in patients with localized scleroderma than in healthy controls. The serum levels of sIL-2R were correlated with the number of sclerotic lesions, the number of involved areas, the levels of anti-ssDNA, and the levels of antihistone antibody immunoglobulin M. Moreover, sIL-2R levels in sera from patients with SSc were also significantly higher than in healthy controls. Elevated serum levels of sIL-2R in localized scleroderma suggest that lymphocyte activation is one of the early processes in the development of this disease.