The objective of this study was to investigate the possible prognostic factors in patients with metastatic colorectal cancer (CRC) treated with protracted venous infusion (PVI) of 5-fluorouracil (5-FU). PVI of 5-FU is considered to be one of the standard therapies for patients with CRC because of its high efficacy and low toxicity, but possible prognostic factors in patients with CRC treated with PVI of 5-FU have not been reported until now. One hundred two consecutive patients with metastatic CRC, treated with PVI of 250 mg/m(2) /d of 5-FU at the National Cancer Center Hospital between January 1991 and December 1998, were investigated retrospectively. The data were evaluated for possible correlations with clinicopathologic indices or prognosis. In this study, grade III nausea, stomatitis, diarrhea, and hand-foot syndrome occurred in only 3%, 5%, 5%, and 6% of cases, respectively. No grade III or more hematologic toxicities were observed. The overall response (complete response + partial response) rate for all 102 cases was 26%, with a 95% CI of 18% to 35%. Overall median survival time for the 102 cases was 303 days. In multivariate analysis, the favorable prognostic factors were normal albumin level (<or=3.7 g/dl), histologic grades I, II, and low carcinoembryonic antigen level (<100 ng/ml).