Glutathione S-transferase mu-1 (GSTM1) is a polymorphic member of the mu class gene family of the glutathione S-transferases. Individuals who are GSTM1 null have increased susceptibility to lung and colon cancer. We hypothesized that: (a) GSTM1 null individuals might also be at increased risk for development of ovarian cancer; and (b) the GSTM1 genotype would influence response to chemotherapy. One hundred and forty-six individuals with invasive epithelial ovarian cancer were genotyped using a three-primer PCR reaction specific for the GSTM1 gene and an internal control glutathione S-transferase mu-4 (GSTM4). The products were analyzed on agarose gels. Healthy individuals without a family history of ovarian, breast, or colon cancer served as unmatched controls (n = 80). The results show that age at diagnosis, histological type, and stage of ovarian cancer were all independent of GSTM1 genotype. The frequency of the GSTM1 null genotype in the ovarian cancer cohort was similar to that in the control population, 51% versus 58%, P > 0.05. Likewise, median survival for individuals with advanced stage ovarian cancer was independent of GSTM1 genotype. We concluded that the GSTM1 null genotype does not increase ovarian cancer risk. These findings suggest that GSTM1 does not play a significant role in detoxifying environmental factors that influence ovarian carcinogenesis and does not play an important role in the resistance of ovarian cancer to chemotherapy.