Activation of ras family genes has been implicated in colorectal tumourigenesis. K-ras is the most frequently altered gene in colorectal neoplasias. The major activating mechanism involves point mutations, although recent data have shown a more complex role, through qualitative alterations. The incidence of codon 12 mutations in K-ras and N-ras genes in patients with primary colorectal adenocarcinomas was examined. We employed a non radioactive PCR-RFLP assay for the detection of mutant samples. We found a significant K-ras activation at codon 12 (38%), while the incidence of N-ras codon 12 activation was limited to 1.5%. These results are in agreement with previous reports. Association has been investigated with clinical and histopathological parameters. Point mutations appear to be more frequent in carcinomas with elements indicating a development from adenoma, in ages below 50 years, in females who had the tumor located at the rest of the large bowel in comparison with rectosigmoid and in higher grade of differentiation.