AIM:To study the diagnostic significance of K-ras genemutations in fecal samples from elderly patients with largeintestinal cancer.METHODS:DNA was extracted in the fecal and tissuesamples from 23 large intestinal cancer patients,20 colonicadenomatoid polypus patients and 20 healthy subjects.TheK-ras gene mutations at the first and second bases of codon12 were detected by the allele specific mismatch method.RESULTS:The K-ras gene mutation was 56.52%(13/23) inthe large intestinal cancer patients,which was notably higherthan that in the normal subjects whose K-ras gene mutationwas 5%(1/20) (x~2=12.93,P<0.001).There was no significantdifference in comparison with that of colonic adenomatoidpolypus patients whose K-ras gene mutation was 30%(6/12)(x~2=3.05,P>0.05).The K-ras gene mutation at the secondbase of codon 12 was 92.13%(12/13) in the large intestinalcancer patients.There was no significant difference betweenthe detection rate of K-ras gene mutation in the fecal andtissue samples (x~2=9.35,P<0.01).CONCLUSION:Our results indicate that detection of theK-ras gene mutations in fecal samples provides a non-invasivediagnostic method for the elderly large intestinal cancerpatients.Its significance in the early diagnosis of largeintestinal cancer awaits further studies.