Hypertrophic osteoarthropathy (HOA) is characterized by finger clubbing, periostosis and arthritis. The pathogenesis of hypertrophic osteoarthropathy is still uncertain. Earlier studies have been focused on the potential role of platelet and endothelium in the pathogenesis of HOA. The aim of this study was to evaluate the circulating levels of endothelin-1 (ET-1), beta-thromboglobulin (beta-TG) and platelet-derived growth factor (PDGF) in 21 HOA patients. The circulating levels of ET-1, beta-TG were significantly higher in HOA patients vs healthy controls, but not vs controls with lung diseases. On the contrary, PDGF was significantly higher in HOA patients vs healthy controls and vs subjects with lung diseases. These findings suggest that "endothelium/platelet unit" may play a role in the pathogenesis of HOA, and PDGF could induce the changes observed in HOA.