This is a prospective, sequential, multi-center, open-label study with subjects on thrice-weekly (in-center) hemodialysis (HD). After a Screening Period, there will be 12 hemodialysis treatments on the Optiflux dialyzer (Optiflux Period), followed by 38 HD treatments on the dialyzer with Endexo (Endexo Period), and then a Follow-up Visit. The study population will consist of End-Stage Renal Disease ESRD subjects who are a minimum of 22 years of age. The primary objective of the study is to collect data on the performance of the dialyzer with Endexo when used to perform hemodialysis (HD) in End-Stage Renal Disease (ESRD) subjects.