In the present study we have evaluated the prognostic significance of ploidy levels and proliferative activity in 279 cases of large bowel carcinomas which were included in a surgical prospective randomized trial. Ploidy levels and proliferative activity were determined on nuclei isolated from paraffin-embedded tissues of 279 colorectal carcinoma patients, with a mean follow-up of 51.9 months. Product limit survival analysis demonstrated a borderline significant association (P = 0.0689 by generalized Breslow; P = 0.0336 by generalized Savage) between ploidy and survival, with a 75th quantile survival of 49.8 months for patients with diploid tumors and 35.9 months for patients with aneuploid tumors. After stratification for staging, Dukes' C cases showed a statistically significant association between tumor ploidy and survival (P = 0.0224 by generalized Breslow, P = 0.0110 by generalized Savage). Product limit survival analysis for proliferative activity and survival showed a similar outcome with the strongest association in Dukes's C stage of disease (75th quantile survival of 38.9 months for low proliferative and 18.0 months for high proliferative tumors).