Fibroblasts are a diverse cell type and display clear topographic differentiation and positional memory. In a screen for fibroblast specific markers we have characterized four monoclonal antibodies to endosialin (TEM1/CD248). Previous studies have reported that endosialin is a tumour endothelium marker and is localized intracellularly. We demonstrate conclusively that endosialin is a cell surface glycoprotein and is predominantly expressed by fibroblasts and a subset of pericytes associated with tumour vessels but not by tumour endothelium. These novel antibodies will facilitate the isolation and classification of fibroblast and pericyte lineages as well as the further functional analysis of endosialin.