Computerized gamma scintigraphy revealed a significant (p< 0.001) rising lung:heart radioactivity ratio, which has been called "slope of injury" or "slope index", with both99mTechnetium-tagged human serum albumin (99mTc-HSA) and99mTechnetium-tagged red blood cells (99mTc-RBC) after 0.05 or 0.2 ml/kg iv oleic acid administration to dogs. This slope index was significantly greater with99mTc-HSA than99mTc-RBC (p< 0.001). These findings verify that the scintigraphic99mTc-HSA slope of injury is a result of a pulmonary capillary protein leak and not oleic acid induced changes in pulmonary blood or air volume. The leak of red blood cells noted with scintigraphy was confirmed by light microscopy and examination of the tracheal edema fluid. The leak of albumin, however, was much greater than the leak of red blood cells by microscopy and tracheal fluid examination, confirming the scintigraphic data. This study provides further evidence that computerized gamma scintigraphy will be of value for the diagnosis of permeability pulmonary edema and its response to treatment.