This review deals with the rationale for the use of hemodilution in patients not subjected to open heart surgery. The claim for an optimum of circulatory oxygen transport at 30% hematocrit has been disproved; hemodilution thus simply means acute normovolemic anemia. Accordingly, it generates a cardiovascular strain and particularly jeopardizes cerebral and myocardial oxygen supply. Potentially serious clinical side effects have been reported. Hemodilution should therefore not be carried beyong the lower normal range for the hemoglobin or hematocrit level, i.e. 12--12.5 g% or 35--36%.