A phase 2 trial of vincristine infusion was conducted in a group of 21 patients with refractory multiple myeloma. Patients were generally heavily pretreated with radiotherapy and chemotherapy. Vincristine was given intravenously (IV) as a 0.5 mg bolus and followed immediately by infusion of 0.25 to 0.50 mg/m2/d for 5 days. Courses were repeated every 3 weeks in the absence of disease progression or prohibitive toxicity. Objective responses (partial) were noted in two patients (10%), both of whom were administered 0.5 mg/m2/d infusions. Response durations were brief (2.2 and 1.2 months). Toxicity consisted of neurotoxicity and myelosuppression. In addition to the occurrence of paresthesias and myalgias, ileus (two cases) and moderately severe loss of motor function (two cases) were observed. The mean lowest WBC count following treatment was 2.67 X 10(3)/microL v 3.96 X 10(3)/microL pretreatment (P = .008). The mean lowest platelet count was 75.0 X 10(3)/microL v 106.8 X 10(3)/microL pretreatment (P = .008). Vincristine infusion appears to have limited activity in the treatment of refractory multiple myeloma. Additionally, response durations were short lived and toxicity, both neurologic and hematologic, was appreciable.