The efficacy and safety of reinduction therapy with gemtuzumab ozogamicin (GO)were investigated in 7 patients with relapsed or refractory CD33-positive acute myelogeneous leukemia. As the administration method, intravenous drip infusion of 9 mg/m(2) was conducted on day 1 and 15. Though CR was attained in 3 patients, the remaining 4 patients were assessed as PD. Grade 3-4 neutropenia and thrombopenia occurred in all patients, 4 of whom were complicated with febrile neutropenia and 1 with new pneumonia. On the other hand, except for grade 1 digestive symptoms and grade 1 GPT increase, none of the patients had serious complications. Though the treatment with GO is considered comparatively safe, sufficient supportive therapy as in the case of conventional chemotherapy is necessary against hematological toxicity. The effect of monotherapy with GO in reinduction is limited. It is necessary to appropriately select the cases and to investigate an effective administration method including the concomitant use of antitumor agent.