OBJECTIVE: Human spermatozoa are rich in polyunsaturated fatty acids and are therefore susceptible to reactive oxygen species attack. To counteract the harmful effects of ROS, seminal plasma prossess a number of antioxidant systems that scavenge ROS and prevent internal cellular damage. We assessed whether any group of infertile men is more likely to have high seminal oxidative stress. DESIGN: Cohort study. MATERIALS AND METHODS: Twenty-one fertile donors and 112 infertile patients were included in the study. We divided our infertile patients into 3 different groups according to the clinical diagnosis: group A, varicocele (n = 62); group B, infection (n = 18); group C, idiopathic infertility (n = 32). Semen characteristics, Catalase, superoxide dismutase (SOD) were assessed in samples from patients with various clinical diagnoses and controls. RESULTS: Sperm concentration, motility, and morphology were reduced in groups A and B compared to the controls (p = 0.04). Lower levels of SOD (14.67 ± 7.27) and catalase (14.87 ± 1.95) were seen in infertile patients compared to fertile donors (SOD = 38.03 ± 21.65) (Catalase = 34.03 ± 20.65) (P = 0.02). Patients in group A have a trend (but not statistically different) to have lower SOD levels (12.2 ± 5.4) and Catalase levels (12.6 ± 1.7) compared to the other groups of infertile men (p = 0.05).Table 1Sperm concentration, motility, and morphology in groups A and B compared to the controlsClinical diagnosisConcentrationMotilityMorphologySODCatalaseControl53.4 ± 5.2259.93 ± 5.3132.05 ± 1.4138.03 ± 21.6534.03 ± 20.65Varicocele19.89 ± 3.77 (p = 0.04)33.2 ± 2.33 (p = 0.04)21.1 ± 4.1 (p = 0.04)12.2 ± 5.4 (p = 0.01)12.6 ± 1.7 (p = 0.01)Infection19.18 ± 6.1 (p = 0.04)29.97 ± 2.43 (p = 0.04)19.12 ± 4.44 (p = 0.04)15.12 ± 8.21 (p = 0.02)16.32 ± 2.12 (p = 0.02)Idiopathic infertility48.53 ± 6.35 (p = 0.1)37.93 ± 3.36 (p = 0.07)31.2 ± 2.65 (p = 0.09)14.9 ± 5.45 (p = 0.02)17.24 ± 1.54 (p = 0.02)Infertile group (Overall)31.2 ± 8.35 (p = 0.06)34.26 ± 3.67 (p = 0.08)23.2 ± 4.56 (p = 0.07)14.67 ± 7.27 (p = 0.02)14.87 ± 1.95 (p = 0.02)P Values compared to controls. Open table in a new tab P Values compared to controls. CONCLUSIONS: Irrespective of the clinical diagnosis and semen characteristics, the presence of seminal oxidative stress in infertile men suggests its role in the pathophysiology of infertility.