We reviewed 48 records of combined blood pool and transmission scans, performed in the last three years for mediastinal masses and cardiomegaly. The purpose was to investigate the diagnostic value of this radioisotopic examination, and in particular to compare it with the roentgenographic examination. The accuracy of both methods in visualizing mediastinal tumors or tissue pathology was very similar. The scintigraphic examination was superior for the diagnosis of cardiovascular pathology. False negative results occurred more frequently than false positives, especially in cases of tumors and aneurysms.