Glutathione S-transferase (GST) isoenzymes are an important superfamily of proteins that are present in homodimer or heterodimer structures. The isoenzymes included in this superfamily are involved in endobiotic and xenobiotic detoxification systems in animals, plants and microorganisms. This compilation focuses on the importance of functional aspects of polymorphic variants in different populations so the risk genotypes can be identified as indicators of disease susceptibility. Genetic studies will help to develop prognostic biomarkers for early prediction and risk assessment in patients, and enable clinicians to develop personalized treatment regimens. The authors examine the different kinds of reactive oxygen species and reactive species which act as carcinogens and cause damage to DNA, RNA, proteins and lipids, thereby resulting in human disease like bladder cancer. Also reviewed is the association of GST's common genetic variants with the development of infertility (failure to establish a clinical pregnancy after 12 months of regular, unprotected sexual intercourse) in women and in men.