Placental glutathione S-transferase (GST-P) may facilitate cell proliferation and inhibit apoptosis, hence allowing for the expansion of a population of initiated tumor cells. The enhanced expression of GST-P at the protein level has been reported previously in chemically induced oral carcinomas in hamster buccal-pouch mucosa but the expression of GST-P at the mRNA level has not yet been demonstrated. The purpose of the present study was to assess the GST-P mRNA expression in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas using a reverse transcription-polymerase chain reaction (RT-PCR). Thirty-five outbred, young (6 weeks old), male, Syrian golden hamsters (Mesocricatus auratus) were randomly divided into one experimental group (15 animals), and two control groups (10 animals each). Bilateral pouches of a group of 15 animals of the experimental group were painted with a 0.5% DMBA solution three times a week for 12 weeks while each animal of one of the control groups was similarly treated with mineral oil. Another control group of 10 animals was untreated throughout the experiment. Areas of dysplasia and squamous-cell carcinomas with a 100% tumor incidence developed in all of the DMBA-treated buccal pouches. The mineral oil-treated and untreated pouches revealed no obvious changes. Placental glutathione S-transferase mRNA was demonstrated to be present amongst all the 12-week DMBA-treated hamster buccal-pouch mucosa animals, but not for the untreated animals or the animals for which the buccal pouch was treated with mineral oil. Multiple potential regulatory pathways including gene amplification, enhanced mRNA stability, chromosomal translocation/gene rearrangement, and hypomethylation of the promoter region can contribute to the overexpression of GST-P mRNA in DMBA-induced hamster buccal-pouch carcinomas. Further study is necessary to completely understand which candidate mechanism(s) will contribute principally to the increased GST-P mRNA expression in oral experimental carcinogenesis.