Thirty infusion studies with Tc-99m-labeled macroaggregated albumin were carried out in 21 patients who had histologically proven peripheral tumors. Three patterns of tumor perfusion were noted: increased central radioactivity in 13 patients, decreased central radioactivity with or without increased peripheral radioactivity in four, and absence of radioactivity in four. In the last category, all four patients had no evidence of tumor neovascularity by contrast angiography. In all 21 patients the intraneoplastic patterns showed very good correlation between contrast angiography and radionuclide angiography. Pulmonary tracer uptake was documented in all 14 patients who had counts performed over the lungs; one had no evidence of tumor neovascularity by either angiographic study, and only 8 of the 13 remaining (61%) showed evidence of appreciable tumor arteriovenous shunting by contrast angiography. Decreased tumor perfusion, presumably due to vessel spasm, was found in one patient.