Patients who underwent curative resection for colorectal cancer between January 1987 and June 1989 were divided into two groups, to assess the usefulness of preoperative chemotherapy (400 mg UFT therapy daily for 10 days more) and to analyze changes in the proliferative activity of tumor cells. Fifty-five cases were included in the study. Thirty-three had received no preoperative chemotherapy (Group A), and 22 had received the preoperative chemotherapy (group B). The five-year cumulative survival rate was 81.1% for group A and 90.2% for Group B. The proportion of patients with no recurrence was 75.7% in Group A and 85.7% in Group B. Both parameters thus tended to be better in patients who had received preoperative chemotherapy. When PCNA labeling before UFT therapy was compared with that after UFT therapy in 13 cases, the PCNA labeling rate decreased after UFT therapy in 9 (69%) of the 13 cases. These results suggest that preoperative chemotherapy using UFT is useful in treating colorectal cancer, and that the proliferative activity of colorectal cancer can sometimes be reduced by such preoperative adjuvant therapy.