Red cells' transfusions are a cornerstone of critical care practice. By the day 3 in the ICU, most of the patients are anemic, due to phlebotomy or due to their clinical condition. A restrictive strategy of red cell transfusion for Hgb values <7gr/dl is effective and well tolerated, with the possible exception of patients with cardiovascular diseases. The age of red 'blood cells transfused is related to the outcome and oxygen delivery of ICU patients. It is not clear if blood transfusions improve the outcome related to mechanical ventilation, even if there are some studies that show improvement in the weaning process of severe COPD patients. The use of EPO reduces the number of blood transfusions and helps to achieve higher Hgb levels. Pneumon 2005, 18(3):298-304.