DNA content and cell proliferation were measured by flow cytometry on paraffin-embedded Stage B2 or C colorectal adenocarcinomas from 694 patients enrolled in adjuvant trials conducted by the North Central Cancer Treatment Group. Patients with diploid tumors had a higher survival rate than those with nondiploid tumors (P less than 0.001). The proliferation index (the sum of the percent of cells in S-phase plus those in G2M phase) was also a strong prognostic factor (P less than 0.001). The ploidy and proliferation data were combined, and the patients in the favorable group (diploid and low proliferative index) had a 5-year survival of 74% compared with 54% for the unfavorable group (high proliferative index or nondiploid, P less than 0.001). This grouping was prognostic for survival in B2 (P less than 0.001), C (P = 0.013), colon (P less than 0.001), and rectal (P = 0.026) patient subsets. This study indicates that cell kinetic parameters are important and independent prognostic factors for Stages B2 and C colorectal cancer.