Back in the 1990s, nitric oxide was named "Molecule of the Year" because of the discovery of its role as a neurotransmitter and the understanding we gained from the discovery with regard to cardiovascular health and male sexual health. Textbooks were subsequently updated. Now a quarter of a century later, they might have to be written again thanks to a discovery by researchers at Cornell University, New York, USA. The work focuses on the nitrogen cycle rather than human physiology but could have global impact. The team has identified a critical step in the nitrification process, which is partly responsible for emissions of nitrous oxides into the atmosphere, which give agriculture a role in global climate change. Current biochemical models say that inorganic hydroxylamine is the only intermediate formed when bacteria convert ammonia from fertiliser into nitrite. But the new work suggests nitric oxide is a second intermediate in this process.