Erythropoietin has become an important part of the treatment of patients with end-stage renal disease (ESRD). Erythropoietin treatment and the concomitant increase in red blood cell mass have been associated with improvements in a variety of important clinical outcomes that bear on the morbidity and mortality of dialysis patients. However, many patients do not reach the target hematocrit goals, and there is a large variation among patients in the amount of erythropoietin administered. A number of potentially modifiable factors influence the response to erythropoietin, including higher delivered dose of dialysis. However, the type of dialysis membrane may modify this association. Preliminary data suggest that the hematocrit level among erythropoietin-treated patients is higher in those dialyzed with a synthetic as opposed to a nonsynthetic dialyzer. This article briefly reviews the relationship among erythropoietin response, dialysis dose, dialyzer type, and other modifiable factors.