Background: Monocyte activation is associated with acute atheromatous plaque disruption and acute coronary syndromes. Angiographically complex coronary stenosis is often an expression of plaque disruption. Increased serum concentration of neopterin, has been observed in patients with coronary artery disease.Objectives: To assess neopterin level in patients with unstable angina and patients with stable angina, and to assess its relation to complex stenosis in patients with unstable angina.Methods: 30 patients with unstable angina, 10 patients with stable angina and 10 healthy subjects were included. Serum neopterin was assessed. Coronary stenosis in patients with unstable angina was assessed and classified as complex or smooth stenosis.Results: Neopterin level was higher in patients with unstable angina. Neopterin was correlated with the number of complex stenosis; it was higher in patients with multiple (three or more) complex stenosis.Conclusion: Neopterin concentration is correlated with the presence of multiple complex stenoses and may represent a marker of coronary disease activity