EPO is a very basic protein stored in and secreted from human eosinophil granulocytes. The main activity of EPO is that of a peroxidase, but other non-peroxidase activities have been identified. EPO is unique to eosinophils. EPO may be measured in various biological fluids as a reflection of the turnover and activity of the eosinophil population in the body. We provide you with the tools to study the involvement of EPO in human disease processes.