Limited hemodilution does not affect the respiratory function of the blood, neither in vitro nor in vivo. By virtue of the unchanged affinity of oxygen for hemoglobin and increase in nutritional flow, reduction in the O2 content of the blood is completely compensated. Tissue hypoxia does not develop as long as pulmonary and circulatory compensation is ensured. As a result, maintenance of a normal blood volume is an essential parameter. Information is not yet available concerning the relationship of O2 supplies in coronary disease. Coronary disease is presently considered to be a contra-indication since a marked reduction in the O2 content of the blood could restric coronary reserves and result in myocardial ischemia.