Twenty-four patients with metastatic breast cancer that had progressed after high-dose chemotherapy with peripheral blood progenitor cell (PBPC) support were given intramuscular methotrexate in combination with oral UFT (tegafur and uracil) and oral leucovorin (the MUL regimen). Of the total treated, 21 patients are currently evaluable for response and toxicity. All patients had received extensive prior chemotherapy, including a high-dose regimen with PBPC support. Of the 21 assessable patients, 8 obtained either a complete response (1) or partial response (7), for an overall objective response rate of 38%. Another 7 patients had stable disease for 3 or more months. Therefore, the MUL regimen was able to stop disease progression for 3 or more months in nearly 75% of patients. The median time to progression and median overall survival from the start of MUL were 6 and 9 months, respectively. The toxicity was mainly gastrointestinal; 6 patients (29%) had World Health Organization grade 2/3 diarrhea, leading to a UFT dose reduction. Emesis was mild and easily manageable with thiethylperazine. In conclusion, MUL chemotherapy is active and well tolerated in patients with metastatic breast cancer in progression after high-dose chemotherapy. Further studies with this regimen, either as salvage chemotherapy or as maintenance chemotherapy after high-dose chemotherapy with PBPC, are warranted.