Several theories have been advanced to explain the mechanisms by which varicocele impairs male fertility. These theories include scrotal hyperthermia, retrograde flow of adrenal or renal metabolites, Leydig cell dysfunction and hypoxia. Varicocele is reported to be associated with elevated reactive oxygen species (ROS) production in spermatozoa and diminished seminal plasma antioxidant activity. The aim of this study was to investigate whether surgical correction of varicocele might reduce ROS or increase the antioxidant capacity of seminal plasma from infertile patients with varicocele. The study group consisted of 68 infertile males, selected from patients scheduled for varicocelectomy at Cairo University Hospital during the year 1999. Seminal plasma levels of two ROS [malondialdehyde (MDA), hydrogen peroxide (H2O2)] and one ROS radical [nitric oxide (NO)] were estimated as well as six antioxidants [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), vitamin C (Vit C), vitamin E (Vit E), albumin) on the day prior to varicocelectomy. For comparison, the same parameters were measured again 3 and 6 months post-operatively. A statistically significant reduction in the 3 month post-operative levels of MDA, H2O2 and NO was observed when compared with the pre-operative values. A further significant reduction took place during the following 3 months. Four of the six antioxidants tested (SOD, CAT, GPx, and Vit C) showed a significant increase in seminal levels when comparing 3-month post-operative with pre-operative values. A further significant increase of the four antioxidant levels took place during the following 3 months. No significant change in the level of seminal plasma albumen took place during the first 3 months after varicocelectomy, however, a significant increase was noted during the next 3 months. In contrast to other antioxidants, seminal plasma levels of Vit E showed a significant decrease when comparing 3-month post-operative with pre-operative values. A further significant decrease took place during the following 3 months. It is concluded that varicocelectomy reduces ROS levels and increases antioxidant activity of seminal plasma from infertile men with varicocele.