 In a preliminary study, it has shown that reticulocyte count kinetics depends on ESAs type, dose and administration frequency. Reticulocyte kinetics were compared in three groups of stable dialysis patients, depending on their ESA treatment. Reticulocyte curves under a monthly Mircera treatment were different from the other ESAs, showing a high reticulocyte peak av. 80 000 reticulocyteml occurring on Day D8-D10 after Mircera administration. On the contrary, at nadirs point D20-D30 after injection, reticulocyte levels are low for all the patients, preventing from any interpretation of the reticulocyte level at monthly routine assessment. It looks as though it is the peak level of reticulocytes that should be used as a marker of ESA response. 