An antisense approach was attempted to investigate the role of antisense GLUT1 RNA in suppressing tumor cell phenotypes using N-ras-transformed NIH 3T3 cells. The established cell line transformed by ras showed typical biological characteristics of cancer cells, such as increased glucose transport, GLUT1 mRNA contents, and the ability to form colonies on the soft agar. In this system, the plasmids (pMAM-GLUT1(rev)) which can transcribe the antisense GLUT1 RNA were transfected and the accompanying changes in the phenotypes of the ras-transformed cells were observed. The expression of antisense GLUT1 RNA by induction with dexamethasone reduced the glucose transport by 30% (1.97 ± 0.13 nmoles) after 4 min incubation when compared to the non-induction group of transformed cell (2.85 ± 0.19 nmoles). Also, the number of colonies sized over 50 microns on the soft agar was reduced significantly in the antisense RNA expressing group compared to non-induction group. These results suggest that the expression of antisense GLUT1 RNA reduced the glucose transport and transforming potential in soft agar possibly by hybridization with GLUT1 mRNA in N-ras-transformed NIH 3T3 cells.