He discovered a substance in endothelial cells that relaxes blood vessels. He called it endothelium-derived relaxing factor (EDRF). He later worked out EDRF's nature and mechanism of action, and determined that EDRF was nitric oxide (NO), which is an important compound in many aspects of cardiovascular physiology. The research that was done was important in explaining the action of Viagra, treatment of blue babies, and other medical as well as health-related issues. He won the Nobel Prize in Physiology or Medicine in 1998 "for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system". He shared the prize with Louis Ignarro and Ferid Murad. He also won a Gairdner Foundation International Award in 1991 and a Albert Lasker Award for Basic Medical Research in 1996.