The efficiency of a molybdenum wire as a catalyst for the nitrogen isotope equilibration reaction, 28N2+30N2= 229N2, has been studied for filament temperatures between 800 and 1900°K and nitrogen pressures between 1.8 × 10–7 and 1.8 × 10–6 torr. The efficiency was essentially independent of pressure and passed through a maximum of about 1.4 % at 1300°K. The reaction took place only when the filament temperature was high enough to cause a measureable desorption of gas from a saturated filament.