a b s t r a c tIntroduction: Reactive oxygen species (ROS) serve several physiological functions. At supraphysiological levels they participate in the pathophysiology of many diseases by damaging biomolecules. In several disease conditions and following exposure to insecticides, pesticides and organic pollutants there is oxidative stress. Psychological stress and depression are known to raise cortisol levels and cause oxidative stress. So, this study was planned with the aim to measure and establish baseline ROS levels in whole blood in normal healthy individuals and to investigate the effect of yoga on ROS levels and 8-hydroxy-2-deoxyguanosine (8-OHdG) levels which is an oxidative DNA damage marker.Method: Whole blood ROS levels was measured in 175 healthy individuals by chemiluminescence method using luminol as a probe. Levels of blood ROS and 8-OHdG were also measured in 50 healthy individuals following a 10 days pretested yoga programme. Statistical analysis was performed using SPSS version 15 software. Results: The median whole blood ROS value in the healthy individuals was 1266.0 RLU/min/ 10 4 neutrophil (Minimum e 573.0; Maximum e 2345.0). The mean ROS levels post yoga (1020.81 ± 0.79 RLU/minute/10 4 neutrophil) was significantly lower (p ¼ 0.024) as compared to pre yoga (1215.07 ± 0.88 RLU/minute/10 4 neutrophil). The 8-OHdG levels post yoga (9367.57 ± 2709.58 pg/ml) was also significantly lower (p < 0.041) as compared to pre yoga (10268.23 ± 3349.71 pg/ml). Discussion: Baseline ROS value in the whole blood can act as a diagnostic tool in various clinical conditions and exposure to several environmental modulators can disrupt ROS homeostasis and life style intervention like yoga can decrease ROS levels.