Twenty patients with refractory multiple myeloma were treated with methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of polyamine synthesis. MGBG 500 mg/m2 was administered on days 1 and 8, and then every 14 days. The dose was escalated to 600 mg/m2 on day 22, as tolerated. Of 14 evaluable patients, none met ECOG criteria for an objective response. The major toxicity was hematologic and related infections. MGBG demonstrated insufficient activity in the treatment of refractory multiple myeloma to warrant further study.