As mutations at codon 12 of the Ki-ras oncogene have been shown to occur in 90% of pancreatic adenocarcinomas, a novel strategy for the detection of these mutations in pancreatic secretions obtained at routine endoscopies was developed. Ki-ras DNA was amplified and screened for the presence of mutations at codon 12 with a combination of different rapid, non-radioactive molecular biology techniques. Examination of DNA from cell lines and paraffin-embedded tumour samples was used to establish and test the strategy employed. Pancreatic secretions from 27 patients were examined for the presence of Ki-ras mutations. Mutations at codon 12 were detected in 16/16 secretions from patients with histologically confirmed carcinoma and from one patient with carcinoma of the bile duct. In six patients a mutation identical to the one found in the pancreatic secretions was also demonstrated in paraffin-embedded fine-needle biopsy or surgical samples. Of the remaining ten patients (who had pancreatitis or cholelithiasis) mutations were not found in nine. Ki-ras codon 12 mutation was identified in one of these patients however, and mucous cell hyperplasia of pancreatic ducts was found upon histological examination. These findings establish Ki-ras polymerase chain reaction from pancreatic secretions as a valuable new diagnostic procedure for the demonstration of malignant cells, possibly at an early stage of the disease.