Recent years, specific antigens of vascular endothelium have been found one after another, and they contribute to progress of vascular biology. This antibody, being unlike any other prior antibodies, reacts especially with arterial microcirculating system including small arteries and blood capillaries, and also reacts with some small venous endothelial cells. This is an unprecedented type (site-specific) of anti vascular endothelium antibody, generated with an adjuvant-induced benignant lymphangioma (intra-abdominal tumor) by "rapid differential immunization technique" (a more efficient immunization method for antigens which are weak in antigenicity.) It doesn't react with endothelial cells of lymph vessels but reacts with some blood cells.