The heterogeneity in the DNA content was analysed in multiple biopsies from the surgical specimens in 77 cases of colonic and 46 cases of rectal adenocarcinomas. Frozen and unfixed tumour tissue was analysed with the flow cytometric technique. A total of 78/123 (63%) of all tumours displayed aneuploid stemlines in one or more pieces of tumour tissue; 45 were homogeneously aneuploid and 33 were heterogeneous, presenting both aneuploid and near-diploid samples. The remaining 45 tumours were homogeneously near-diploid. The heterogeneity in ploidy tended to be slightly higher if ten as compared with four samples from each tumour were analysed. Ploidy correlated to localization in the bowel and gender, but not to age, histopathological tumour stage, tumour differentiation or to the resectability rate for cure. The mean value of the S-phase fraction was 17% (range 7-31%) in the near-diploid and 14% (range 8-20%) in the aneuploid tumours. The range of the intratumoural variation was small for the DNA index (at most 5%) and high for the S-phase fraction (19% for near-diploid and 24% for aneuploid tumour pieces). Neither the mean value nor the heterogeneity in the DNA index and in the S-phase fraction displayed any correlation with the studied characteristics. In conclusion, the ploidy and the S-phase fraction varied considerably both within and between the tumours. As a consequence, multiple sampling is mandatory for a correct classification of colorectal adenocarcinomas based on the DNA content.