Class pi-glutathione S-transferase (GSTP-1) is one of several factors proposed to affect drug sensitivity to cisdiamminedichloroplatinum (II) (CDDP). It has also been investigated as a potential marker for the serodiagnosis of various types of cancers. In this study, attempts were made to quantify mRNA levels of the enzyme in healthy and cancerous gastric mucosa specimens, and to evaluate their significance in inherent drug resistance to CDDP. Thirty gastric cancer specimens were analysed by northern blotting with radiolabelled GSTP1 cDNA. Of these, the chemosensitivities of 22 specimens were evaluated by the succinic dehydrogenase inhibition (SDI) test. GSTP-1 mRNA was detected in all the specimens, with slightly increased, but non-significant expression in the neoplasms. Comparison of these drug sensitivities with results of northern blotting analysis showed no inverse correlation, as was expected from the widely investigated role of the enzyme in drug resistance.