Pancreaticobiliary maljunction (PBM) patients have a high incidence of cancer in the gallbladder. In the present study, we showed that precancerous lesions in the gallbladder of PBM such as hyperplasia or metaplasia, indicated high concentration of the amount of total mRNA. The mRNA content could be easily measured by our new technique utilizing a GenePlate, which is a poly (dT) oligonucleotide immobilized plastic plate, and Yoyo-1, a fluorescent DNA intercalator. To standardize the mRNA contents, we utilized <mRNA index> which was defined as the ratio of total mRNA contents to total nucleic acids in a same sample. The mRNA index of the proliferating cells was significantly higher than that of the resting cells, and the mRNA index of cancer cells, such as gastric cancer, colon cancer, bile duct cancer, and gallbladder cancer also showed significantly higher concentration than that of normal mucosa. In the study of precancerous lesion, PBM, the mRNA index was significantly higher than that of mild cholecystitis but less than that of gallbladder cancer, suggesting that in the gallbladder mucosa of PBM, a precancerous state was able to be diagnosed by the mRNA index.