Our data have shown that the positive rates of MGMT, ERCC1, hMSH2, and hMLH1 were significantly lower in pancreatic ductal adenocarcinoma than in non-cancerous pancreatic tissues of rats, and the ductal epithelia of non-cancerous pancreas which had negative expression of MGMT, ERCC1, hMSH2, and hMLH1 all shown atypical-hyperplasia. The gene discussed is MLH1; the disease is pancreatic ductal adenocarcinoma.