Analysis of cell kinetics may be beneficial for evaluation of the therapeutic effect of anticancer agents. Therefore, using flow cytometry, the authors could classify perturbations of DNA histogram of cultured colon cancer cells treated with 5-FU into 4 types. Perturbation of DNA histogram of cancer cells treated with 5-FU of different concentrations was closely associated with the degree of cell damage indicated by the growth curve. Then, tumor samples before and after injection of 5-FU were collected from 9 preoperative patients with colon cancer and classified into the above 4 types. The results show that 2 cases were classified into type I (S/G1 ratio: 1.5 greater than, G1.G2M comparison: G1 greater than G2M) and another two into type IV (CV ratio: 1.5 less than or equal to, S/G1 ratio: 1.5 less than or equal to, G1.G2M comparison: G1 greater than G2M). However, 5 cases could not be classified (not evaluated) because of the absence of stemline and the presence of heterogeneity in tumor samples. The authors consider that the classification of perturbation of DNA histogram is a useful method to evaluate the degree of cell damage with 5-FU, if tumor samples are appropriately selected and analysis is made with careful attention.