Phase II studies of vinorelbine (Navelbine; Burroughs Wellcome Co, Research Triangle Park, NC; Pierre Fabre Médicament, Paris, France) have been conducted mainly at a dose of 30 mg/m2/wk, and this schedule has been used extensively in the treatment of advanced breast cancer. Vinorelbine used in a first-line setting as a single agent in 25 patients with previously untreated advanced metastatic breast cancer produced objective responses in 15 patients (60%) and complete responses (CR) in five (20%). A large multicenter study to assess the response rate by the main site of disease involvement included 145 assessable patients. The overall response rate was 41% (10 CRs and 50 partial responses: skin, 70%; lymph nodes, 67%; primary tumor, 56%; lungs, 33%; measurable bone, 27%; and liver, 23%). The median time to disease progression was 25 weeks and the median overall survival duration was 18 months. Neutropenia was the principal toxicity with grade 3/4 suppression noted; however, this was not accompanied by serious infection (incidence of grade 3/4 infection < 1%). Other grade 3/4 toxicity also was uncommon. Another phase II study included 50 patients assessable for toxicity and response. The overall response rate was 50% (2% CRs). In a salvage setting (second- and third-line treatment), 33 patients were treated with an overall response rate of 30% (two CRs). Rates of toxicity were no greater than in first-line patients. The most notable results for combination vinorelbine therapy were with a schedule of vinorelbine 25 mg/m2 on days 1 and 8 and doxorubicin 50 mg/m2 on day 1, with cycles repeated every 21 days. The overall response rate for the 89 evaluable patients was 74% (19 [21%] CRs; 47 [53%] partial responses). These data indicate that vinorelbine is a highly active agent with a favorable toxicity profile in the treatment of breast cancer.