Our aim was to determine GSTT1 expression levels in left colon tumors and paired normal tissue in orderto identify specific alterations in GSTT1 mRNA levels. Alterations in GSTT1 expression in twenty-four leftsidedcolon tumors and paired cancer free tissue were determined by qRT-PCR. Significant fold changes weredetermined with t-test. When compared with cancer free tissue, left colon cancers showed a significant decreasein GSTT1 expression. However, GSTT1 mRNA levels among different grades increased gradually in correlationwith tumor grade. Our results suggest that downregulation of GSTT1 in left-sided colon cancers is an early eventand is reversed with cancer progression, probably due to cellular defense mechanisms as a response to changesin the microenvironment.