p53 expression, DNA ploidy and S-phase fraction were analysed retrospectively in colorectal adenocarcinomas from 293 patients in whom the long-term outcome was known. The frequency of nuclear p53 staining was increased in non-diploid tumours (42%) when compared with diploid tumours (33%). Cytoplasmic p53 positive tumours were more common in the proximal colon (32%) than in the distal sites (21%). In univariate survival analysis, nuclear p53 and cytoplasmic staining were significantly associated with poor prognosis in patients with Dukes' A-C tumours. The patients showing both nuclear and cytoplasmic p53 staining had the poorest survival and the patients with tumours negative in both the nucleus and cytoplasm showed the best prognosis. The patients with tumours positive in the nucleus alone or in the cytoplasm alone presented an intermediate survival. In multivariate survival analyses, nuclear p53 expression, cytoplasmic p53 expression and DNA ploidy were prognostic indicators independent of Dukes' stage and each other. Further analysis suggested that the prognostic importance of cytoplasmic p53 expression was greater in diploid than in non-diploid tumours. We conclude that nuclear p53 expression, cytoplasmic p53 expression and DNA ploidy provide important prognostic information in colorectal adenocarcinomas.