Ninety-two patients with advanced breast carcinoma and no prior chemotherapy from 65 to 90 years old were treated with the combination cyclophosphamide (C), methotrexate (M), and 5-fluorouracil (F) (CMF). Because of the primary renal excretion of the first two drugs, their initial doses were calculated using a linear function of creatinine clearance. 5-Fluorouracil was given at 2/3 of the usual dose. These doses resulted in no significant age trends in almost all toxicity, response, time to failure, or cycle by cycle percentages of calculated dose actually received. There was significantly less nausea and vomiting as age increased (P less than .001) and patients greater than 80 years had a significantly shorter survival (P = .01) than patients aged 65 to 79 years. The toxicity results are in marked contrast to the experience of 126 patients aged 24 to 65 years treated with usual doses of CMF on earlier protocols. Among these younger patients there was a significant upward trend with age in diarrhea (P less than .001) and noticeable upward trends with age in hematologic toxicity (P = .06), infection (P = .06), and severe mucositis (P = .09). Patients greater than 65 years had their doses decreased less quickly than did patients less than 65 years; hence by the sixth cycle, the young and elderly patients were receiving almost the same amount of M and F.