Purpose: To find out whether the polymorphism at GSTM1, GSTT1 and GSTP1 loci is associated with increased susceptibility to glaucoma. Methods: We genotyped 153 primary open angle patients and 159 healthy controls. Genomic DNA from peripheral blood was examined using polymerase chain reaction and defined for the genetic polymorphisms of glutathione S-transferase. Results: The frequency of the GSTM1 null genotype individuals among the glaucoma patients was significanlty higher than in controls (54.9 vs 40.9%) with odds ratio of 1.64 ( 95% CI: 1.10 - 2.59). The frequency of the GSTT1 and GSTP1 in both groups were not statistically different. Conclusion: The present study suggests that the GSTM1 null genotype may be a genetic risk factor for development of primary open angle glaucoma. Further associations studies in other polymorphic genes for xenobiotic - metabolizing enzymes are needed to elucidate the environmental-genetic interaction in the underlying cause of primary open angle glaucoma.