Chronic inflammation associated with tumor necrosis factor (TNF)-α and reactive oxygen species (ROS) is the hallmark of tuberculosis. Mycobacterium tuberculosis (MTB) directly stimulates human monocytes to secrete TNF-α. We show the augmented expression of TNF-α mRNA in MTB-infected monocytes by cellular activation and ROS was suppressed by allicin in a dose-dependent manner. Also, allicin enhanced the glutathione peroxidase activity, which correlated inversely with the downregulation of ROS and TNF-α in MTB-infected monocytes. Hence, allicin may prove to be a valuable natural antioxidant in combating tuberculosis. © 2006.