Background: Mycobacterium tuberculosis (MTB)is the causative organism of the chronicrnbacterial infection, tuberculosis (TB). TB is one of the leading causes of death due torninfectious diseases worldwide. Recently it has been observed that arginase (ARG)-is nornlonger a mere enzyme responsible only for urea cycle but is a key enzyme that plays a greatrnrole in modulation of the immune response and thus, pathogenesis. Infection with MTB andrnother intracellular pathogens induces the activation of ARG and inducible nitric oxidernsynthase (iNOS) which competitively metabolize L-arginine as a common substrate tornproduce L-ornithine and nitric oxide (NO), respectively. ARG induced deprivation of Largininernis important for pathogens to limit the intracellular production and killing action ofrnNO and T cell responses. Therefore, induction of ARG might be an important escapernmechanism for the survival of MTB.rnMaterials and Methods: A cross-sectional study was carried out to compare the level ofrnARG activity in the saliva, plasma and peripheral blood mononuclear cells (PBMCs)ofrnnewly diagnosed HIV sero -negative smear positive TB patients (n=18) and healthy controlsrn(n=8). The level of arginase activity in all type of samples was measured by enzymatic assayrnand a two-tailed Mann-Whitney U test was performed to assess statistical differences.rnResults: There was a statistically significantly higher level of arginase activity in thernPBMCs (p=0.015)and saliva (p=0.008)of TB patients than those of healthy controls.rnFurthermore, an increased level of arginase activity was detected in the plasma of TBrnpatients as compared to healthy controls, however it was not statistically significantrn(p=0.211). A significantly higher (p=0.024)frequency of arginase expressing cells wererndetected in the PBMCs of TB patients as compared to healthy controls. The phenotype ofrnthese cells was identified as CD15rn+rnneutrophile.rnConclusions and recommendation: Infection with MTB can result in an increasedrnfrequency of ARG-expressing cells as well as in increased level of arginase activity in thernPBMCs, saliva and plasma of the TB patients. Therefore, the measurement of ARG activityrnin saliva might be used as a biomarker of TB infection.