Reactive oxygen species (ROS) levels in semen are believed to play both physiological and pathological roles in male fertility. The study was aimed to find the clinical significance of ROS levels in infertile Indian men. This pilot study included 33 idiopathic infertile men and 18 proven fertile controls. ROS levels in the washed sperm were measured using chemiluminescence assay and expressed as 10(6) cpm per 20 million spermatozoa. Sperm count, percent sperm motility, and percent normal sperm morphology were found to be significantly (P < 0.0001) reduced in infertile men compared with the controls. Median (minimum, maximum range) ROS levels of the infertile group [24.90 (6.89, 44.71)] were found to be significantly (P < 0.0001) elevated compared with the fertile controls [0.167(0.15, 2.78)]. No significant correlation was seen between ROS levels and semen parameters. Elevated ROS levels in the idiopathic Indian infertile men may be one of the underlying reasons for impaired fertility. Therefore measurement of seminal ROS levels may be used in Indian infertile men for better understanding of the aetiology and selection of antioxidant regimen in the treatment of male infertility. However, large studies may be urgently warranted to find out the role of antioxidants in ROS elevated Indian infertile men through randomised, controlled clinical study.