BACKGROUND: Although vascular endothelial growth factor (VEGF)-A/VEGF receptor 2 (KDR) signalling may play a major role in the microangiopathy of systemic sclerosis (SSc), serum levels of soluble KDR (sKDR) in this disease have not yet been determined. OBJECTIVES: To evaluate the possibility that serum sKDR levels can be a specific disease marker of SSc. METHODS: Serum sKDR levels of 42 patients with SSc, 10 patients with Raynaud's phenomenon (RP) and 22 healthy controls were measured with specific enzyme-linked immunosorbent assays. Quantitative real-time polymerase chain reaction (PCR) was performed to determine KDR mRNA levels. RESULTS: In females, the serum sKDR levels were significantly higher in patients with SSc, especially limited cutaneous SSc, than in patients with RP or healthy controls. Quantitative real-time PCR with RNA from skin sections revealed that KDR mRNA levels were also increased in the skin of patients with SSc with elevated serum sKDR levels. A significantly lower prevalence of pulmonary fibrosis, higher percentage vital capacity, and a higher incidence of telangiectasia were seen in female patients with SSc with elevated serum sKDR levels than those with normal levels. CONCLUSIONS: These results suggest that the skin can be one of the sources of elevated serum sKDR levels, and that serum sKDR levels are useful for diagnosis and may be a marker of microangiopathy in patients with SSc, especially females. The VEGF-A/KDR signalling system may be involved in the pathogenesis of the disease.