Experiments were conducted with the aim of deriving quantitative indexes from radiographs that describe the status of the pulmonary vasculature under hypervolemic doncitions. Hypervolemia was induced in four baboons by the infusion of dextran solution. Left ventricular pressures were monitored in the erect animals during the infusion and radiographs were obtained. The radiographs subsequently were digitized with a scanning laser-densitometer and a PDP 11/40 minicomputer. An index was derived (the vascular complexity index, Cx), which combined the mean density difference between upper and lower lung zones (indicative of incipient pulmonary edema) and the ratio of density variations in the upper versus lower zones (indicative of redistribution of blood flow). The data indicate a good correlation between left ventricular and diastolic pressure and Cx during the infusion in each animal.