Scientists at the Pacific Northwest National Laboratory in Richland, Wash., have used an established technique to observe real-time interactions between single protein molecules for the first time. Ultimately, the PNNL method – single-molecule photon stamping spectroscopy – will be used to study signaling events in living cells. At present it offers more information about protein-protein interaction dynamics than can be obtained with conventional structural biology techniques such as nuclear magnetic resonance (NMR) and X-ray crystallography.