The invention relates to covalently cross-linked mammalian hemoglobins, to which polyalkylene oxides are covalently linked. Such hemoglobins are surprisingly compatible with proteins of human and animal plasma, under all the possible conditions within the vascular system of the body. The invention furthermore relates to the production of these cross-linked hemoglobins linked with polyalkylene oxides, as well as to their use as artificial intravasal oxygen carriers in the human or animal organism or in individual organs.