Nitrification inhibitors were successfully used to improve the recovery of fertilizer N in the irrigated cotton-growing system. By slowing the rate of nitrification of applied ammonium-N, it was shown that the loss of N through denitrification was limited by the reduced concentration of nitrate in the soil. The effectiveness of recognised and experimental nitrification inhibitors to inhibit nitrification and reduce N loss through denitrification were compared in field and laboratory experiments. The more effective inhibitors (2-ethynylpyridine (2-EP), Terrazole and N-Serve) were able to reUird nitrification for more than 8 weeks. They also improved N fertilizer recovery (from 35 to 50% in one situation) and enabled the cotton crops to better utilise fertilizer N where denitrification loss was severe. In some instances, lint yields were increased significantly (up to 18%) to where the profitability of cotton-growing was substantially improved.