We examined 82 surgically resected or biopsied, formalin-fixed, paraffin-embedded primary adenocarcinomas of the pancreas for the presence of activating point mutations in codon 12 of the K-ras oncogene. Mutations were detected using primer-mediated, mutant-enriched, polymerase chain reaction-restriction fragment length polymorphism analysis and characterized further by allele-specific oligonucleotide hybridization. This combination of mutant-enriched polymerase chain reaction-restriction fragment length polymorphism analysis and allele-specific oligonucleotide hybridization results in a rapid and sensitive characterization of the mutations in codon 12 of K-ras. Sixty-eight (83%) of the 82 carcinomas examined harbored a point mutation. Of the 68 mutations, 33 (49%) were guanine to adenine transitions, 27 (39%) were guanine to thymine transversions, and eight (12%) were guanine to cytosine transversions. Mutations were found in carcinomas of the head (61 of 75, 81%) as well as in carcinomas of the body or tail (seven of seven, 100%) of the pancreas. The overall prevalence of K-ras point mutations in adenocarcinomas of the pancreas obtained from patients who smoked cigarettes at some point during their lives (88%; 86% in current smokers and 89% in ex-smokers) was greater than that seen in pancreatic adenocarcinomas from patients who never smoked cigarettes (68%, P = 0.046). The presence of K-ras point mutations did not correlate with tumor ploidy, tumor proliferating index, or patient survival. These results demonstrate that primer-mediated, mutant-enriched polymerase chain reaction-restriction fragment length polymorphism analysis combined with allele-specific oligonucleotide hybridization can be used to detect and characterize mutations in codon 12 of the K-ras oncogene in formalin-fixed, paraffin-embedded tissues, and the results confirm that activating point mutations in codon 12 of the K-ras oncogene occur frequently in adenocarcinomas of the pancreas.