Preoperative autologous blood donation (PAD) is a commonly used technique for elective surgical procedures with a predictable blood loss. The conventional method is to collect one unit whole blood weekly several times within the shelf-life of red cell concentrates. Erythrapheresis with the Haemonetics cell separator MCS-3p or plus ® makes it possible to collect two units of red cells in one single session and with this option the time interval and operation can be prolonged to three weeks to improve erythropoiesis. 295 patients, who were scheduled for hip replacement or knee endoprothesis were evaluated retrospectively calculating the net profit of red cells after donating two units of red cells by erythrapheresis. The median net profit of red cells was 140 ml red cells but with a wide range. The patients who profit most of PAD were those with a predonation hct below 42% who had net profits up to 300 ml red cells due to an increased erythropoiesis, which compensate for the withdrawal of the red cells. Thus erythrapheresis with the Haemonetics MCS-3p ® or Haemonetics MCS plus ® is recommended for patients with a predonation hct lower than 42% and who can be scheduled for PAD at least 3 weeks before operation when two units of red cells are the target for PAD.