The relationship between varicocele and male infertility remains to be explained. Oxidative damage because of the testicular venous backflow may represent one of the causes of gonad injury and seems to precede the histological alteration. Therefore measuring the values of spermatic or intratesticular nitric oxide (NO) could be useful in evaluating this oxidative distress. The aim of this study is to assess the role of testicular NO in early detection of the damages induced by an experimental varicocele in the Wistar rat. A left varicocele was induced in 10 animals (group A). A control group of 10 rats was performed (group B). Animals were killed 3 months after the operation. Both testicles were harvested, weighed and sectioned in two equal parts: one for the evaluation of the NO level and the other one for histological examination. All the rats in group A showed a conspicuous dilatation of the left spermatic vein. The histopathological analysis was normal in both the groups. Biochemistry showed a meaningful statistical difference (P < 0.001) in the concentrations of NO among the specimens of the left and right gonads in group A but no difference was found in group B. The increase in NO values and the presence of other oxidant agents represent the first sign of testicular distress and it seems to anticipate histopathological changes. As it is well known that a great difference exist between human and animal sperm, NO could therefore in the future be taken into consideration together with others parameters for the evaluation of patient who is affected by varicocele.