To evaluate the dose-response effect of an adjuvant anthracycline-based non-taxane chemotherapy in early breast cancer patients. This was a retrospective database analysis. Selection criteria included patients treated for early breast cancer from years 1980 to 2000 with an adjuvant anthracycline-based non-taxane chemotherapy. The delivery of chemotherapy was assessed through the number of delayed cycles, the number of delayed days and the relative dose intensity (RDI) administered (>or= 85%, <85%). Seven hundred and ninety-three breast cancer patients were included. The Kaplan-Meier disease-free survival (DFS) was affected by the number of delayed cycles (P<0.0001), the number of delayed days (P<0.0001) and the RDI (P=0.0029). The Kaplan-Meier overall survival (OS) was also affected by the number of delayed cycles (P=0.0008) and days (P=0.0115), as well as the RDI (P=0.0055). The Cox regression models showed that, when the number of nodes affected and the hormonal receptor status were controlled, all the study variables maintained their significance on DFS, but not on OS. The dose-response effect is a crucial factor in the administration of anthracycline-based non-taxane schedules for the adjuvant treatment of early breast cancer. Delays and/or reductions of chemotherapy should be avoided if possible to achieve the maximal benefit.