['The aim of this study was to investigate whether the glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) gene polymorphisms contributed to development of gestational diabetes mellitus (GDM).', 'Fifty women with diagnosis of GDM and 50 control individuals without GDM or altered glucose intolerance during their pregnancy were enrolled in the study. Multiplex polimerase chain reaction-restriction fragment length polymorphism method was applied to determine the GSTM1 and GSTT1 gene polymorphisms. Genotypes were determined according to bands detected with the agarose gel electrophoresis.', 'The difference in the frequencies of GSTM1 null genotypes between GDM and control groups was not statistically significant (60% and 54%, respectively). There was no statistically significant difference between GDM and control groups with respect to GSTT1 null genotype rates (22% and 20%, respectively).There was no statistically significant difference between GDM and control groups with respect to GSTT1 null genotype rates (22% and 20%, respectively).'] Are glutathione s-transferase m1 and t1 gene polymorphisms associated with increased risk of gestational diabetes mellitus development?