Objective: This present study was undertaken to determine the levels of malondialdehyde (MDA), nitric oxide (NO) and total antioxidant status (TAS) in testes of adolescent rats with experimental bilateral varicocele and to determine the effects of oxidative stress on testis produced by varicocele. Methods: 6-week-old, male Wistar rats, weighing 146 - 334 g (228.37 +/- 41.34 g), were randomly allocated into two groups. The first group underwent selective and bilateral partial ligation of the spermatic vein (n = 28), and the second group underwent a sham operation and served as the controls ( n = 15). Animals were sacrificed 12 weeks after surgery and dilatation of the spermatic veins was observed in the first study group. Bilateral orchiectomy was performed in all rats, and MDA, NO and TAS levels were measured. Results: In the study group, the mean MDA (SEM) level was 15.58 +/- 6.07 mumol/g protein, and in the control group, it was 11.59 +/- 3.86 mumol/g protein, respectively; this difference was statistically significant (p < 0.05). The mean NO level was 82.73 +/- 77.84 nmol/g protein in the study group, whereas 28.65 +/- 20.18 nmol/g protein in the control group, this difference was also statistically significant (p < 0.005). The mean TAS levels of the study and control groups were 0.91 +/- 0.32 and 1.78 +/- 0.46 nmol/g tissue, respectively, and this difference was also statistically significant ( p < 0.001). But there was no correlation between these three parameters (MDA &LRARR; TAS: r = - 0.103, p > 0.05; MDA <----> NO: r = - 0.104, p > 0.05; NO <----> TAS: r = - 0.123, p > 0.05). Conclusion: These findings suggest that varicocele may change the testicular oxidative status and may play a role in testicular dysfunction that causes infertility. Copyright (C) 2004 S. Karger AG, Basel.