Gemtuzumab ozogamicin was recently approved in the United States for the treatment of older patients with CD33-positive acute myeloid leukemia (AML) in first relapse. However, the lack of randomized clinical trials makes it so difficult to determine which patients are best suited for this compared with other treatment regimens. Results for 128 patients given gemtuzumab ozogamicin in phase II trials were compared with those for 128 patients given high-dose cytarabine (HDAC) combination therapy in different trials Multivariate logistic regression was used to analyze age, duration of first complete remission (CR1), and cytogenetics for potential differences between the groups. rare of overall remission )combined complete remission [CR] plus CR with incomplete platelet recovery [CRp]) following treatment with gemtuzumab ozogamicin or HDAC therapy were 38% and 41%, respectively. Gemtuzumab ozogamicin treatment was associated with a higher overall remission rate compared with HDAC treatment if CR1 duration was 3-10.5 months. In contrast, HDAC treatment was associated with a higher overall remission rate than gemtuzumab ozogamicin treatment if CR1 duration was >19 months. If CR1 duration was between 10.5 and 19 months, the differences in treatment responses were not statistically significant. Thee results reflect the much stronger treatment than with gemtuzumab ozogamicin treatment. Early death (occurring within the first 6 weeks of therapy) was less likely in patients <45 years of age after ADAC and was less likely in patients >75 years of age after gemtuzumab ozogamicin treatment. These data support the recommended use of gemtuzumab ozogamicin as monotherapy in older patients with AML in first relapse, but caution against this use in patients, particularly younger ones, with a long duration of CR1.