Towards better understanding EPOR trafficking properties, as well as properties of EPOR mutants harbored by PFCP patients, we presently have developed a novel panel of rabbit monoclonal antibodies to the hEPOR, and have used these new tools to study wild-type and truncated human EPOR expression, distinct molecular-weight forms, subcellular localization, activation, and trafficking in EPO- dependent human erythroid progenitor cell models. Here, EPOR is linked to primary familial polycythemia due to EPO receptor mutation.