For nearly two decades, scientists have appreciated the healing power of nitric oxide (NO), a free radical that garnered researchers at three U.S. institutions the 1998 Nobel Prize in Physiology or Medicine for their discoveries involving NO as a signaling molecule in the cardiovascular system. Despite its promise, NO’s potential has been limited by the fact that the substance is gaseous and highly reactive, confounding the ability of drug developers to store and deliver it safely in the right amount, to the right location and at the right time.