Estimates have been made of the amounts of nitrogen dioxide (NO2) in the operating room of University of Benin Teaching Hospital (UBTH) where nitrous oxide (N2O) a potential source of NO is used as an anaesthetic agent Measurements were made using palmes diffusion tubes, a device which is capable of taking samples of NO2 gas from the atmosphere through diffusion or permeation of this compound to the interior and subsequently trapping it by means of adsorption on reactive material, but which does not involve the active movement of the gas through the sampler. Results obtained indicate a low concentration of NO2 in the operating room with a minimum of 5.83 microg/m3 and a maximum concentration of 6.22 microg/m3 NO2. This result therefore suggests that the use of nitrous oxide in the operating room does not contribute significantly to the concentration of NO2.