Erythroferrone (ERFE) is a glycoprotein hormone secreted by erythroblasts inresponse to erythropoietin stimulation. ERFE suppresses the hepatic synthesis of the master iron-regulatory hormone, hepcidin. The impact of erythropoiesis stimulation on ERFE secretion in humans is poorly understood. This paucity of information is due in part to the lack of available means for ERFE quantification in serum samples. The present study tested a new sensitive sandwich immunoassay for human ERFE. This assay was used to demonstrate that injection of various erythropoiesis stimulating agents (ESAs) increased the blood ERFE levels in healthy volunteers. After exogenous stimulation of erythropoiesis, ERFE increased up to 8-fold with a detection window of 13 days. The impact of one unit of blood withdrawal on erythropoiesis stimulation of ERFE was also tested. ERFE significantly increased after blood withdrawal in subjects injected with both iron and saline solution, suggesting that iron supplementation did not mask the ERFE increase after blood withdrawal. The effects of exercise-induced muscle damage on ERFE was assessed by comparing ERFE levels with creatine kinase levels in samples from subjects with heavy exercise loads, and determined that this was not a confounder. The ERFE assay is a sensitive means to investigate the connection between iron metabolism and erythropoiesis in humans, and to detect ESA abuse in the antidoping field. K E Y W O R D Sblood doping, erythroferrone, immunoassay