Analysis of the DNA extracted from the colonic mucosa of 13 patients operated for colorectal carcinoma revealed c-myc rearrangements in three of them. In all cases, the alterations were found both in the histologically normal and in the tumoral mucosa. In one case, a different pattern of rearrangements characterized the two tissues. In all three individuals, the c-myc sequences appeared to be amplified. We suggest that c-myc rearrangements in the histologically normal colonic mucosa of colorectal carcinoma patients could represent a predisposition factor for the development of additional neoplasms.