Using Cox's proportional hazard model, we performed a multivariate analysis of survival data from 126 patients who underwent curative resection for colorectal cancer from 1971 to 1985. Flow cytometric DNA measurements were carried out using paraffin wax-embedded tissue blocks. Fifty-four per cent of the cases were found to be aneuploid and 46% were diploid. The depth of invasion of the tumor, nodal status, liver metastasis, peritoneal dissemination, DNA ploidy pattern, histology, macroscopic classification of the tumor, age, sex and site were tested in a survival analysis. The initial seven factors were found to be the significant prognostic variables in a univariate analysis. A multivariate analysis shows liver metastasis, DNA ploidy pattern and peritoneal dissemination as being the significant discriminants of survival (P = 0.0001, 0.0022, 0.0119, in this order). Therefore, nuclear DNA ploidy pattern in colorectal cancer is considered to be an independent prognostic factor.