The expression of glucose transporter genes (GLUTI-4) was studied in 20 head-and-neck tumors of 18 patients. All tumors--16 of which were squamous-cell carcinomas (SCC)--expressed GLUT1 and/or GLUT3 mRNA, while detectable levels of GLUT2 or GLUT4 mRNA were not observed. The signals for GLUT1 and GLUT3 mRNAs varied markedly throughout the SCC tumor population but no clear relationship with the grade of differentiation was found. The high GLUT expression observed in some tumors was not associated with amplification or rearrangement of the corresponding genes. Immunohistochemistry of 5 SCCs showed that GLUT1 protein was located in tumor-cell membranes in relation to the level of mRNA expression. We conclude that both GLUT1 and GLUT3 are involved in basal glucose uptake of extracranial head-and-neck tumors. The increased expression of these high-affinity GLUT isoforms may be related to the growth maintenance of cancer tissue in cases of limited supply of substrate e.g., in poorly vascularized tumor areas.