Glutathione S-transferases (GSTs) catalyze the conjugation of glutathione to numerous potentially genotoxic compounds. The GSTM1 gene codes for the enzyme glutathione S-transferase-mu, the GSTT1 gene codes for the enzyme glutathione S-transferase-theta, and the GSTP1 gene codes for the enzyme glutathione S-transferase-pi. GSTM1 is polymorphically expressed, and three alleles have been identified (GSTM1-0, GSTM1a, and GSTM1b). Two functionally different genotypes at the GSTT1 locus have been described. Individuals with homozygous deletions of GSTM or GSTT have reduced or no glutathione S-transferase activity and therefore may be unable to eliminate electrophilic carcinogens as efficiently. However, results of epidemiologic studies do not confirm associations between GSTM1, GSTT1, and GSTP1 and epithelial ovarian cancer.