Glutathione S-transferases (GSTs) are enzymes involved in the detoxification of several environmental mutagens, carcinogens, and anticancer drugs. GST polymorphisms resulting in decreased enzymatic activity have been associated with several types of solid tumors. We determined the prognostic significance of the deletion of 2 GST subfamilies genes, M1 and T1, in patients with acute myeloid leukemia (AML). Using polymerase chain reactions, we analyzed the GSTM1 and GSTT1 genotype in 106 patients with AML (median age, 60.5 years; range, 19-76 years). The relevance of GSTM1 and GSTT1 homozygous deletions was studied with respect to patient characteristics, response to therapy, and survival. Homozygous deletions resulting in null genotypes at the GSTM1 and GSTT1 loci were detected in 45 (42%) and 30 (28%) patients, respectively. The double-null genotype was present in 19 patients (18%). GST deletions predicted poor response to chemotherapy (P =.04) and shorter survival (P =.04). The presence of at least one GST deletion proved to be an independent prognostic risk factor for response to induction treatment and overall survival in a multivariate analysis including age and karyotype (P =.02). GST genotyping was of particular prognostic value in the cytogenetically defined intermediate-risk group (P =.003). In conclusion, individuals with GSTM1 or GSTT1 deletions (or deletions of both) may have an enhanced resistance to chemotherapy and a shorter survival.