Objective: Cytokines, nitric oxide (NO) and reactive oxygen species (ROS) are well known for their pathogenic effects in development of cardiovascular diseases. Interleukin-1β (IL-1β) is known to induce NO generation, however it is not well established if IL-1β or NO regulate production of ROS, such as superoxide anion. Therefore, the main objective of this study was to evaluate the effect of IL-1β or NO on enzyme activity of NADPH oxidase (NOX), a superoxide-generating system recently documented to participate in a variety of vascular functions. Methods: Human coronary artery smooth muscle cells (SMC) obtained from Clonetics were treated with IL-1β and NO donor, sodium nitroprusside (SNP), in culture. Nitrites accumulated in supernatants of SMC cultures were measured as an index of NO released following treatment with IL-1β. NOX enzyme activity was assayed using cytochrome c as the electron acceptor. Results: Treatment with IL-1β resulted in a 3-fold increase in the production of NO by SMC. Both IL-1β and SNP enhanced NOX activity, by 67 and 45%, respectively, following 24 h of treatment. Conclusion: This study suggests that NO or NO- generating cytokines might regulate the production of ROS in the cardiovascular system through modulation of superoxide-generating systems such as NOX.