Eniluracil is an effective inactivator of dihydropyrimidine dehydrogenase, the initial and rate limiting enzyme in the catabolism of fluorouracil. The current study was done to determine the objective tumour response of a 28-day oral regimen of eniluracil-fluorouracil in patients with advanced breast cancer.This was a multicentre, phase II study in patients with anthracycline-refractory (AR) or anthracycline- and taxane-refractory (ATR) advanced breast cancer. Oral eniluracil (10 mg/m2) and fluorouracil (1 mg/m2) were taken twice daily for 28 days of each 35-day treatment course.In this study, 106 patients received treatment: 62 patients in the AR stratum and 44 patients in the ATR stratum. The objective tumour response rate in the intent-to-treat population was 18% (95% confidence intervals (CI): 11%-27%), including three complete responses. The response rate was similar in both strata: 19% in the AR and 16% in the ATR stratum. The overall median duration of response was 23.6 weeks. The treatment was well tolerated with a low incidence of grade 3 or 4 toxicities that were considered attributable to study medication.Treatment with oral eniluracil-fluorouracil was well tolerated by patients with advanced breast cancer. The efficacy data were comparable with those of other published studies in this group of refractory patients.