Summary. The present paper deals with analyses of blood within the scope of large-scale experiments with transplanted artificial hearts in cattle.There are undertaken tests on the corpuscular elements of blood, oil plasma proteins as well as on isoenzymcs of lactic dehydrogenase and of peroxidase. There are also proved the factors of clotting system. Moreover, cross tests between erythrocytes and plasma of transplanted animals and canned blood were done, if necessary.As results, among the blood corpuscles there was found a striking changement of the crythrocytes' morphology, further, a numerical diminution of all corpuscular systems of blood, especially of thrombocytes, among the plasma proteins frequently a dysproteinaemia with fibrinogenaemia, among the isoenzymes of lactic dehydrogenase an increase of LDH I, concerning the peroxidase activity an ascendancy of the enzyme fraction within the initial hours after connection with the heart-lungsmachine, and among the clotting factors especially a prolongation of the thromboplastine time and a reduction of the fibrinogen's concentration.The cross tests showed agglutinating reactions in 15 % of all samples and haemolysis in two cases of all.These findings on blood factors may be interpreted as an expression of the injury of the different portions of blood by the plastics' surfaces as well as by changes of haemodynamic forces of streaming blood caused by the pumping function of the heart-lungs-machine. Untersucht wurden die corpuscul/~ren Elemente des Blutes, die Plasmaproteine, sowie die Isoenzyme der Lactatdehydrogenase und der Peroxidase. Aullerdem wurden die Gerinnungsfaktoren bestimmt. Des weiteren sind Kreuzproben zwischen dem Blur der Versuchstiere und der jeweils bereitgestellten Konserven vorgenom° men worden.