We have investigated the correlation between the in vitro chemosensitivity to 5-FU, measured using the collagen gel droplet embedded culture drug sensitivity test (CD-DST), and the anti-tumor effect of UFT, a prodrug of 5-FU, in metastatic tumors from orthotopic implanted colon cancer in nude rats. Human colon cancer cells (KM12SM) were injected into the cecal wall of the nude rats. Five weeks later, the implanted cecal tumors were removed. Oral UFT (a daily dose of 30 mg/kg) was administered postoperatively for four weeks. After the UFT administration period, the lung and lymph nodes were analyzed macroscopically and microscopically. In vitro chemosensitivity to 5-FU in the lung and lymph node metastases was tested using CD-DST, and the enzymatic activities of thymidine synthetase (TS) and dihydropyrimidine dehydrogenase (DPD) in the lung and lymph node metastases were measured. A daily administration of UFT produced an inhibitory effect on lung metastasis compared with the control group. However, there was no difference in the frequency of lymph node metastasis. The inhibition rate produced by 5-FU in CD-DST was significantly higher for lung metastases than for lymph node metastases. There was no difference in the TS and DPD activities between the metastatic tumoral tissues. These results suggest that the organ specificity of the anti-tumor effects of UFT on colon metastases may be determined by CD-DST of 5-FU for individual tumors. The TS and DPD activity in the tumoral tissues may not affect the organ specificity of the anti-tumor effect of UFT on colon metastases.