Murine monoclonal antibody E9 recognises a transforming growth factor (TGF) beta receptor, which is expressed in increased amounts by activated endothelial cells. In order to examine the biological role of this molecule in atherosclerosis, we have measured levels of the TGF-beta receptor alongside those of two other endothelial cell products (von Willebrand factor and soluble E-selectin) in the serum of 55 patients with atherosclerosis (29 with ischaemic heart disease and 26 with peripheral vascular disease), and in a cohort of 26 age- and sex-matched asymptomatic controls. There were increased levels of the TGF-beta receptor (P = 0.0079) and von Willebrand factor (P = 0.0001), but not soluble E-selection in patients' serum relative to the controls. In multivariate analysis of the endothelial cell products against total cholesterol, high density lipoprotein cholesterol and low density lipoprotein cholesterol, triglycerides, systolic and diastolic blood pressures, age, sex and smoking, both the TGF-beta receptor and von Willebrand factor correlated with total cholesterol (Spearman's r = 0.37 and r = 0.35, respectively, both P < 0.001). Lack of a correlation with a coarse endothelial damage marker von Willebrand factor or soluble E-selectin (produced by immunologically stimulated endothelial cells) implies other mechanisms are responsible for increased levels of the TGF-beta receptor in serum of patients with atherosclerosis.