X-radiation has been shown to produce nitric oxide (NO) and nitrogen dioxide (NO2) in the presence of nitrous oxide (N2O). The purpose of the present study was to confirm how much NO and NO2 was produced when constant amounts of nitrous oxide were exposed to constant X-radiation. Twenty polyethylene bottles (capacity 10 litres) were filled with nitrous oxide alone. Another 20 bottles were filled with nitrous oxide and 30% oxygen. Each bottle was placed at a distance of 30 cm from the X-ray tube and they were directly in the line of the X-ray beam at a setting of 90 kV at 0.5 mA, a standard setting for chest fluoroscopy. The range of duration of X-ray exposure was from 0 (control), to 2, 3, and 5 minutes in five bottles each, respectively. A colorimetric recording method (Saltzman) and a chemiluminescent monitor were used for measurement of NO and NO2. In the bottles filled with nitrous oxide alone, the production of NO was not affected by the duration of X-ray exposure, but the longer duration of X-ray exposure produced a larger amount of NO2. In the bottles filled with nitrous oxide and 30% oxygen, the longer duration of X-ray exposure produced larger amounts of both NO and NO2. These finding confirmed a previous investigation in which nitrous oxide was not inert under X-ray exposure. As the presence of oxygen plays an important role in the oxidation of nitrous oxide under X-ray, this study suggests another potentially hazardous interaction that may occur secondary to the administration of an anaesthetic in the presence of X-irradiation such as pulmonary angiography, cardiac catheterisation, and fluoroscopic bronchoscopy or biopsy.