This invention relates to the use of hypo-oncotic aqueous solutions of molecularly dispersed chemically modified high molecular weight crosslinked hemoglobins, namely so-called hemoglobin hyperpolymers, to prepare agents for the symptomatic, primarily life-saving treatment of acute pulmonary edema. Administration in particular is intravascular. Surprisingly, additive administration can be performed since according to the invention the colloidal-osmotic (=oncotic) pressure of the blood itself is essentially raised only slightly, and the blood volume is increased hardly at all. Administration pursuant to the invention is thus (almost) volume-neutral based on the blood into which the injection is made. A hyperpolymeric hemoglobin derivative is thus used therapeutically for the first time as a blood additive for the treatment of pulmonary edema.