The purpose of our research was to develop a stable murine cell line that could serve as a general model for the study of microvascular endothelial cells. To do so we have characterized an endothelial cell line originally derived from a mouse hemangioendothelioma. Endothelioma cells synthesize angiotensin-converting enzyme, express surface receptors for acetylated low density lipoprotein, produce thrombospondin and show intracellular staining with an antibody to von Willebrand antigen. The response of endothelioma cells to endothelial cell mitogens, known angiogenesis-inducing factors, extracellular matrix substrate (Matrigel), and various cytokines was measured. Endothelioma cells show an increased proliferative response to extracts from hypothalamus but only marginally to recombinant fibroblast growth factor or purified endothelial cell growth factor. Rearrangement of cells forming tube-like connections were induced by Matrigel. The chemokinetic responses generally correlated with angiogenesis-inducing properties of the test substances. The results support the conclusion that the endothelioma cell line maintains characteristic endothelial cell properties and behaves in vitro in a manner similar to microvascular endothelial cells.