ABSTRACT Background : Several experimental animal studies suggest the good link between endothelial vasomotor function and the pathobiological process of instent restenosis (ISR). We hypothesized that decreased nitric oxide (NO) bioavailability may increase the risk of ISR. Objectives: This study aimed to evaluate the relation between the plasma level of nitric oxide metabolites (nitrite and nitrate) as an indicator of NO bioavailability and the risk of ISR after coronary stenting. Methods: 103 post stenting patients were grouped according to presence or absence of ISR to G1 and G2 in addition to 15 healthy controls (G3). % diameter stenosis (%DS) and ISR rates were assessed using QCA after 9 months of coronary intervention using bare-metal stent (BMS). Plasma nitrite and nitrate were also measured. Results: ISR rate was 41.7% (representing group 1), negative correlation beteen plasma nitrite, nitrate, HDL, and ISR (p<0.001, <0.001, 0.05) respectively, while positive correlation between hs-CRP, %DS, stented segment length and ISR (p<0.001, <0.05, <0.05) respectively. Low plasma nitrite and nitrate increase the ISR risk 3 and 5 times (P <0.01, < 0.01) respectively. After adjustment for the other different predictors using multivariate regression models; low plasma nitrite and nitrate levels were powerful predictors of ISR (P <0.001, <0.001) respectively. Conclusion: Low NO bioavailability is an independent predictor of ISR at 9 month follow up following coronary intervention (using BMS). We recommend further studies using either drugs improving NO. bioavailability or through coating of stents with a slow release form of NO-donor to evaluate their impact on ISR rates.