The expression of five facilitative glucose transporter genes, GLUT1 (erythrocyte type), GLUT2 (liver type), GLUT3 (brain type), GLUT4 (muscle/fat type), and GLUT5 (small intestine type), was examined in human cancer tissues of the digestive system by RNA blotting analysis. The amounts of the GLUT1, GLUT2, and GLUT3 transcripts were elevated in most cancer tissues studied, although the expression of the GLUT2 gene is primarily restricted to the liver. On the other hand, mRNA levels of GLUT4 and GLUT5 were below sensitivity in all cancer tissues examined. These results suggest that over-expression of GLUT1 and GLUT3 might be closely related with tissue development and that the acceleration of glucose uptake by transformed cells may result, at least in part, from the increase in the expression of these two glucose transporters.