At present, the rapid progress in science and technology around artificial oxygen carriers has advanced to a critical stage.Therefore, it can be assumed that these substances will be clinically available as substitutes for red blood cells within the next years. It can be expected that the major impact of hemoglobin- and perfluorocarbon-based oxygen carriers will be on the use as intermittent blood substitutes during or anticipating acute blood loss from surgery or trauma. However, further applications for artificial oxygen carriers are emerging which cannot fullfilled by red blood cells. Clinical studies are testing now the therapeutic abilities of artificial oxygen carriers in renal anemia, transplantation medicine, cancer therapy, sickle cell disease, treatment of septic shock, treatment of stroke, reduction of air embolism during cardiopulmonary bypass, and as an adjunct to respiratory therapy (‘liquid ventilation’) . In addition, use of artificial oxygen carriers in animal experiments aims at the improvement of oxygen supply in the microcirculation of organs suffering from ischemia. For the long term, biological engineering may increase desired pharmacologic properties of artificial oxygen carriers and widen their spectrum of indications.