OBJECTIVE Pancreatic neoplasm, which is considered as one of the most malignant tumors in humans, is now increasing steadily in frequency. The 5-year-survival rate is less than 5%. In order to detect it in early stage, we tried to analyze K-ras mutation in pancreatic juice collected during ERCP after injection of secretin. Mutation of coden 12 in exon 1 of K-ras gene was reported as high as 90% in pancreatic cancer, but much less in benign pancreatic disease. METHODS 47 patients at Peking Union Medical College Hospital between 1994 and 1998 were enrolled. Pancreatic juice collected during ERCP after injection of 100u secretin, was briefly centrifuged and the sediment was resuspended with PBS. Pancreatic juice supernatant and pancreatic cells were stored at -80 degrees C separately. DNA of the cells and supernatant of the juice were extracted. K-ras point mutation was investigated in the DNA of these supernatant and cells by means of two-stage polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP). RESULTS When the supernatant of the pancreatic juice was used, the PCR successful rate was 82%, K-ras mutation rate of the pancreatic carcinomas was 71% (15/21) compared with 0% (0/7) in benign pancreatic disease (3 chronic pancreatitis, 3 insulinoma and 1 pancreatic cyst). When the centrifuged pancreatic cells were used, the successful rate increased to 96%, sixty-five percent (11/17) of pancreatic carcinomas had K-ras mutation; mutation was also detected in 1/7 of the cases with benign pancreatic diseases (an insulinoma). In total, 78% (21/27) of the cases with pancreatic carcinomas has mutant alleles compared with 8% (1/13) of the benign pancreatic diseases (P < 0.001) when pancreatic juice was used to detect K-ras gene point mutation. In terms of the location of the pancreatic cancer, K-ras mutation rate was not statistically different between the head (80%) and the body + tail (75%). The mutation rate did not vary with the size of the tumor. CONCLUSIONS Detection of coden 12 of K-ras mutation in pancreatic juice can be used in differentiating pancreatic carcinomas from benign pancreatic diseases. It has high sensitivity and specificity.