One hundred and fifty colorectal adenomas were investigated in order to detect the presence of K-rasgene mutation. The adenomas were classified according to the severity of the histological lesion (mild, moderate, or severe dysplasia and carcinomatous transformation) and to the degree of aneuploidy. K-rasmutation was found in 30.8% of cases, mostly consisting of a point mutation of codon 12. K-rasmutation was more frequently found in adenomas >1 cm and in the villous type. No correlation was otherwise demonstrable with the ploidy pattern of the lesion.