Objectives: The potential influence of automated red cell exchange (ARCE) on endothelial activation is not well established. This study was intended to assess whether ARCE influences circulating endothelial cells (CECs) in patients with sickle cell disease. Background: Automated red cell exchange (ARCE) has been used to protect the patient from complications of sickle cell disease. However, the expected benefits vary in different patients. CECs reflect endothelial activation. We hypothesize that suppression of endothelial activation may be an important mechanism of ARCE.