OBJECTIVE: To investigate the potential protective effect of L-glutamine as an antioxidant against the toxic effects of the pesticide deltamethrin (DLM) by examining biochemical and histopathological parameters in the rat ovary. STUDY DESIGN: The rats included in this study were divided into 4 groups (n=10) as follows: Group I, controls (distilled water, 10 mL/kg, p.o.); Group II, Lglutamine (1.5 g/kg, p.o.); Group III, DLM (35 mg/ kg, p.o.); and Group IV, DLM (35 mg/kg, p.o.)+Lglutamine (1.5 g/kg, p.o.). Biochemical measurements were taken and apoptotic changes were determined in ovarian tissue. Immunohistochemical expression of proliferating cell nuclear antigen and CD34 were assessed. RESULTS: Histopathological examination revealed germinal epithelial thinning and degeneration in antral follicles as well as apoptotic changes in the DLM group. The same examination showed significantly elevated estradiol (E2) levels and decreased total oxidant status levels in the DLM+L-glutamine group as compared to the control group (p=0.047 and p=0.048, respectively). Bivariate analysis resulted in the observation that E2 levels correlated negatively with follicular degeneration and vascular hemorrhage (r=-0.471* [p=0.036] and r=-0.482* [p=0.031], respectively) as well as with CD34 expression in preantral and antral follicles (r=0.537** [p=0.005]). CONCLUSION: L-glutamine as an antioxidant might alleviate the toxic effect of the pesticide DLM. © Science Printers and Publishers, Inc.