We previously reported mRNA expression of glutathione S-transferases theta (GSTT)-1, wild type (623 bp) and mutant (500 bp), in patients with myelodysplastic syndrome (MDS). The deletion of 123 bp creates a sequence that is homologous to the mammalian target of rapamycin (mTOR). To analyze the function of mutant GSTT-1 gene, stable transformants for the mutant and wild-type GSTT-1 gene, respectively, were established. In this study, the expression of the wild and mutant type of the GSTT-1 gene of those stable transformants in cell lines and in bone marrow cells from MDS patients by reverse-transcription polymerase chain reaction (RT-PCR) was observed in the presence or absence of rapamycin. Significant growth inhibition by rapamycin was observed among stable transformants for the mutant GSTT-1 gene, but not wild type GSTT-1 gene, and was indicative of typical apoptosis.