Hector Battifora mesothelial-1 (HBME-1) is an anti-mesothelial monoclonal antibody that recognizes an unknown antigen on microvilli of mesothelioma cells. It stains normal mesothelial cells as well as epithelial mesotheliomas in a thick membrane pattern. This antibody also reacts with some (20-30%) carcinomas showing cytoplasmic immunostaining.