We measured serum levels of circulating intercellular adhesion molecule-1 (cICAM-1) in patients with systemic sclerosis (SSc) and normal controls. The levels of cICAM-1 were determined by sandwich enzyme-linked immunosorbent assay in sera from 88 patients with SSc and in 20 healthy controls. In addition, these levels were examined in the supernatants of cultured peripheral blood mononuclear cells (PBMC) and dermal fibroblasts from 10 patients with SSc and 10 healthy control subjects. Serum levels of cICAM-1 were significantly higher in patients with SSc than in healthy controls. Serum cICAM-1 levels were significantly higher in patients with diffuse cutaneous SSc (dcSSc) than in patients with limited cutaneous SSc (lcSSc). These serum levels were correlated with the presence of contracture of phalanges, pulmonary fibrosis, joint involvement and increased erythrocyte sedimentation rate. The release of cICAM-1 was significantly increased in the supernatants of cultured PBMC from patients with SSc. Moreover, inflammatory cytokines (interferon-gamma, interleukin-1 and tumor necrosis factor-alpha) enhanced the release of cICAM-1 in vitro in SSc cells. These findings suggest that cICAM-1 may be involved in immune reactions in this disease.