The correlations between mRNA expressions of 5-fluorouracil(5-FU)-related enzymes; thymidylate synthase(TS), dihydropyrimidine dehydrogenase(DPD), thymidine phosphorylase(TP), and orotate phosphoribosyltransferase (OPRT)in breast cancers, along with disease-free survival(DFS), were investigated in 35 patients treated with postoperative adjuvant chemotherapy using cyclophosphamide, methotrexate and 5-fluorouracil(CMF). The patients treated with CMF were divided into two groups, a lower group(L group)and a higher group(H group), according to the median value of the mRNA expression for each enzyme in 220 breast cancer specimens, which were resected between 1996 and 1998 in our institute. 5-year DFS was not significantly different between TS-L and H group(60% and 80%, p=0.38), DPD-L and H group(57.9% and 86.7%, p=0.088), and TP-L and H group(70% and 73.3%, p=0.89), respectively. 5-year DFS in the OPRT-H group(88.9%)was significantly better than that in the OPRT-L group(50%) (p=0.024). In the OPRT-H group, despite the fact that the proportion of patients with lymph node involvement in the CMF group was significantly higher than that in the postoperative adjuvant hormone therapy group, 5-year DFS was not significantly different between the two groups(p=0.10). Our results suggest that OPRT level was the significant predictive marker for DFS in the breast cancer patients treated with postoperative adjuvant chemotherapy using CMF.