Oxidative stress plays an important role in the development of infertility secondary to varicocele. We aimed to investigate the dynamic thiol-disulphide homeostasis as an oxidative stress marker in the spermatic vein of infertility secondary to varicocele. Sixty-one patients with varicocele were included in the study. Blood was drawn from the median cubital vein and the testicular venous return side before the spermatic vein was separated during surgery. Total thiol, native thiol, disulphide, ischaemia modified albumin (IMA) and albumin values were measured from both the dilated spermatic vein and the median cubital vein. The disulphide/native thiol, disulphide/total thiol and native thiol/total thiol ratios were determined. The mean age of the patients was 27.0 +/- 6.68 (15-50) years. While the albumin, native thiol and total thiol values and the native thiol/total thiol ratio were significantly lower (p = 0.004, p < 0.001, p < 0.001, p < 0.001 respectively), the IMA value and the disulphide/native thiol and disulphide/total thiol ratios were significantly higher (p < 0.001, p < 0.001, p < 0.001 respectively) in the samples taken from spermatic venous blood. Thiol-disulphide balance had deteriorated towards disulphide formation in the spermatic vein compared with the peripheral vein. Abnormal thiol-disulphide balance may be an independent risk factor for infertility secondary to varicocele.