['Hemangioblastoma and metastatic renal cell carcinoma (RCC) may show striking histologic similarities, and the distinction between these two tumors can be difficult. Both occur in middle age, and both occur with increased incidence in von Hippel-Lindau disease (vHL). GLUT1 is an erythrocyte-type glucose transporter protein that is highly expressed by endothelia in brain--but not most peripheral--microvasculature, and by tumor cells in many epithelial malignancies. GLUT1 is expressed by endothelial cells in juvenile hemangiomas, and endothelial GLUT1 expression has been reported for 2 hemangioblastomas arising in a single patient with vHL.', 'We performed immunoreactions for GLUT1 on archival hemangioblastomas from 12 patients (one with vHL), and on RCCs metastatic to brain of 9 patients.', 'Hemangioblastomas showed intense endothelial GLUT1 reactivity in 11/12 tumors resections; the only GLUT1-negative tumor was one for which only previously frozen material was available for immunoreaction, and this tissue showed poor GLUT1 immunoreactivity of internal erythrocyte controls. Hemangioblastoma stromal cell reactivity was found in only 1 case, and was weak and focal. RCCs, in contrast, showed no intralesional endothelial GLUT1 reactivity, but did show intense tumor cell membrane reactivity in 9/9 cases.'] Do gLUT1 immunoreaction patterns reliably distinguish hemangioblastoma from metastatic renal cell carcinoma?