Aerobic exercise draws energy mainly from biochemical processes requiring oxygen, whereas anaerobic exercise draws energy from processes not requiring oxygen.20 healthy male athletes aged (18-24 yrs.) were recuited for this study. Healthy low active males and BMI matched participants (n=10) aged (20-22 yrs.) wererecuited as controls. Aerobic and anaerobic testing was performed on a cycle ergometer. The testing wasa modification of AstrandRhyming protocol forVo2max. Pulserate estimation,Rbcs,Wbcs, HB and hematocrit were estimated using coulter counter. Lactateby accusport, CD34+ stem cells were determined by flow cytometry. Results indicated:VO2 max was increased in case of aerobic exercise bout compared to anaerobic one.Lactate concentration was decreased in case of aerobic exercise bout compared to anaerobicone.Hb, Rbcs,Wbcs and hematocrit were increased after both exercise bouts.CD34+ stem cells were increased in case of anaerobic exercise bout than aerobic one. It is concluded that Vo2 max increased in case of aerobic exercise bout compared to anaerobic one due to the longer period of cycling. Lactate concentration was decreased in case of aerobic exercise bout compared to anaerobic one due to the higher intensity expressed in anaerobic bout leading to decrease oxygen .CD 34+ HPC counts were increased in peripheral blood of anaerobic exercise bout than aerobic one due to stress induced by anaerobic exercise bout .