Glutathione S-transferase (GST) is a part of the most important enzymatic systems protecting organisms from toxic, electrophilic compounds. Expression of numerous GST isoenzymes is changed in various pathological conditions, including neoplasia. The aim of present study was to analyze the expression pattern of GST pi, mu (mu4 and mu5) and alpha at the mRNA and protein levels in human primary gliomas. The studies were conducted on tissue samples obtained from surgery. RESULTS There were no changes in GST pi mRNA expression, determined by RT-PCR, between gliomas and tumor adjacent tissues. However, using Western blotting method, an increase in GST pi protein in tumors was observed, which might be caused by the lower rate in protein degradation. Decrease in the expression of GST mu at mRNA level (mu4), as well as at protein level was shown in gliomas compared to control tissues. mRNA for GST mu5 isoform was demonstrated only in two tumor cases, but not in normal tissues, and for GST alpha, in one sample of control tissue. At the protein level, GST pi expression was increased in gliomas, whereas GST mu was decreased. CONCLUSIONS Changes in GST isoenzymes expression can play an important role in the susceptibility of central nervous system to carcinogenesis.