Glutathione-S-transferase (GST) in one of several factors that are proposed to affect tumor sensitivity to anticancer drugs, including cisplatin (CDDP). Attempts are made herein to evaluate the significance of the enzymes in resistance to CDDP in clinical samples of gastric cancer. A total of 22 gastric cancer specimens, 16 of which were obtained with matching normal mucosae, underwent immunoblotting with polyclonal antibodies against GST-alpha and GST-pi. At the same time, the chemosensitivity of 15 gastric cancer specimens to CDDP was evaluated by the succinic dehydrogenase inhibition (SDI) test. The expression of GST-pi was detected in all the specimens, and its content in the neoplasms exhibited a significant positive correlation with that in the matched normal mucosae. The expression of GST-alpha was detected in 18 of 22 cancer specimens (82%), but its content in the neoplasms did not correlate with that in the matched mucosae. A comparison of the drug-sensitivity findings with the results of immunoblotting revealed a weak but interesting correlation between the protein levels of GST-alpha and CDDP resistance. The cellular content of GST-alpha correlated weakly with CDDP resistance in gastric cancer, and its quantification could contribute to prediction of the clinical effects of CDDP in patients with gastric cancer.