Glutathione S-transferase (GST, EC 2.5.1.18) is one of the most important enzymes protecting cells against toxic, electrophilic compounds. It occurs in isoenzymes, expression of which changes in various pathological conditions including neoplasia. The aim of the present study was to analyze the expression pattern of GST pi, mi4 and alpha in human tongue and floor of mouth squamous cell carcinomas. The studies were conducted on tissue samples obtained from surgery. RT-PCR was used to determine the GSTs-mRNA expression, and Western blotting to study GST pi protein expression. Indicated statistically significant differences in GST pi mRNA expression in tumor and control tissues. GST pi expression was raised in tumors on both mRNA and protein levels, whereas mRNA-GSTmi4 and alfa expression was diverse. Increased level of GST pi expression indicates its role in carcinogenesis.