C-myb structural alterations were analysed by Southern blot hybridization in 55 adenomatous polyps and 21 adenocarcinomas of the colon. Gene amplification was observed in 8 cases (14.5%) and c-myb rearrangements in 3 cases (5.4%) of the preneoplastic lesions analysed. A higher percentage of c-myb abnormalities (23.8%) was shown by malignant tumors. As far as mutant p53 protein is concerned, it was detected both in sera of adenoma and adenocarcinoma patients, though at different levels. No statistically significant correlations were found between c-myb or p53 abnormalities and clinico-pathological variables.