Defective sperm function is the most common cause of infertility, and until recently, it was difficult to evaluate and treat. Part of this difficulty was due to our incomplete understanding of the factors contributing to normal and abnormal sperm function leading to male infertility. Mammalian spermatozoa membranes are rich in high unsaturated fatty acids and are sensitive to oxygen induced damage mediated by lipid peroxidation. Limited endogenous mechanisms exist to reverse these damages. The excessive generation of reactive oxygen species (ROS) by abnormal spermatozoa and by contaminating leukocytes (leukocytospermia) has been identified as one of the few defined etiologies for male infertility. In a normal situation, the seminal plasma contains antioxidant mechanisms which are likely to quench these ROS and protect against any likely damage to spermatozoa. However, during genitourinary infection/inflammation these antioxidant mechanisms may downplay and create a situation called oxidative stress. In addition, aging and environmental toxicants are also likely to further induce this oxidative stress. Assessment of such oxidative stress status (OSS) may help in the medical treatment of this male factor infertility by suitable antioxidants.