Molecular emission cavity analysis (meca) was used for the determination of nitrate and nitrite at trace levels. Nitrite and nitrate were reduced to NO by KI and VCl3 solution, respectively. NO was transferred to the cavity and its emission was measured by a photomultiplier tube. The calibration curve was linear in the range of 2-500 and 560-1200mgmL-1 nitrite and 2-30 and 40-200mgmL-1 nitrate. The detection limit of nitrate and nitrite were 0.6mgmL-1, and 0.2mgmL-1, respectively. The method was applied successfully to the determination of nitrate and nitrite in meat products, and nitrate in tap water and human blood serum. In order to evaluate the reliability of the proposed method, some synthetic samples were also analyzed. The effects of some interfering ions on the determination were also investigated.