INTRODUCTION: In periodontal diesases,inflammatory stimuli increase production of nitric oxide which causes detrimental as well as beneficial role. AIM: 1) To assess the level of NO(nitric oxide) in serum in chronic periodontitis and healthy patients 2) To correlate these levels with the severity of periodontitis. MATERIAL AND METHOD: Two group selected:Group I Healthy subjects without chronic periodontitis and other systemic diseases .Group II Chronic periodontitis patients.Blood sample was collected.Concentration of nitric oxide measured in serum by griess reagent. RESULT: The results of our study showed a higher value in the serum levels of NO(nitric oxide) in group II when compared to group I with mean values (1.23±0.04) μM/50 µl, (0.013±0.004) μM/50µl respectively. CONCLUSION:Nitric oxide level in serum is incresed in chronic periodontitis patients than healthy patients