Vindesine (VDS) at a dose of 1.2 mg/m2/day was administered by intravenous drip infusion for five days to advanced breast cancer patients with multiple organ metastases who had developed a clinical resistance to various chemotherapeutic agents. The blood concentration of VDS was determined serially by radioimmunoassay, and the anticancer effect and side effects were evaluated. Of the 31 patients selected for this study, 29 were eligible, and the treatment was effective (complete or partial remission) in 11 (38%). There was, however, no correlation between clinical effects and VDS blood concentration. Continuous VDS administration induced various side effects, but all were controllable. Blood concentration was correlated with side effects. Continuous intravenous administration of VDS is considered to have a therapeutic effect on advanced breast cancer which has developed resistance to multiple-drug therapy including adriamycin.