This phase II study was designed to evaluate the safety and efficacy of weekly docetaxel (36 mg/m) for the treatment of metastatic breast cancer in 47 frail and/or elderly patients who were ineligible for the standard 3-weekly docetaxel (100 mg/m) regimen. Reasons for ineligibility to the latter were age > or = 70 years (10 patients), poor hematological reserves (15 patients), impaired liver function (eight patients), intolerance to previous taxanes administered 3-weekly without demonstrated resistance (five patients) or any combination of these reasons (nine patients). There was a median of two prior chemotherapy regimens and more than 60% had a WHO performance score at baseline of 2-3. A total of 408 weekly administrations were given over a period of 525 weeks (78% of the intended dose intensity) and the median cumulative dose of docetaxel per patient was 278 mg/m. The incidence of serious adverse events was low. Grade 3 neutropenia occurred in six patients and grade 4 in four patients. Of these 10 patients, eight had pre-existing hematological abnormalities and four developed neutropenic fever. Neurotoxicity was mild and grade 3 paraesthesia occurred in one patient. The overall objective response rate in 37 evaluable patients was 30% and responses were observed in all subgroups of patients. We conclude that weekly docetaxel (36 mg/m) is active, safe and well tolerated in heavily pre-treated frail/elderly patients with poor prognostic features, including low performance scores and multiple metastatic sites, who would not be eligible for treatment with the standard 3-weekly regimen.