Acute normovolemic hemodilution (ANH) entails the removal of blood from a patient either immediately before or shortly after induction of anesthesia and the simultaneous replacement with cell-free fluid, preferably synthetic colloids with a predictable volume effect (6% dextran 60/70, 6% hydroxyethyl starch 200,000 and 130.000, respectively). Hemodilution is part of the concept for avoiding or limiting the use of allogeneic blood and should be considered for patients undergoing elective surgery free of contraindications and presenting with an initial hemoglobin concentration > or = 12 g/dl and an anticipated blood loss of > or = 1500 ml. The efficacy of ANH, judged by the necessity to transfuse homologous blood, depends on the preoperative (initial) hematocrit, the target hematocrit (to which hemodilution is performed), and the preset intra- and postoperative transfusion trigger. In the past data from clinical trials have shown that in healthy subjects a target hematocrit of 20-25% (7.0-8.0 g/dl hemoglobin concentration) is feasible and safe for the patient. The lower the target hemoglobin concentration, the more extensive monitoring is required: intraoperative target hemoglobin concentrations of 5.0 g/dl and less have been tolerated by young surgical patients without adverse effects. The safety as well as efficacy of acute normovolemic hemodilution in terms of reducing homologous blood transfusion requirements have been demonstrated in various clinical studies. ANH therefore is regarded an integral part of programs aimed at reducing the need for homologous blood, and can thus be successfully combined with preoperative autologous blood deposition, intraoperative blood salvage and carefully adjusted surgical techniques.