Mass spectrometry is a crucial tool for the identification of proteins and other biomolecules in biological samples. In recent years, methods for measuring the mass of individual molecules have been reported, but these methods cannot follow the assembly of protein complexes in real time and are limited to relatively large protein complexes. On page 423 of this issue, Young et al. (1) use light scattering to detect and measure the mass of individual unlabeled biomolecules that they had adsorbed from solution to a glass surface. The method allows for the direct detection of proteins as they assemble into functional complexes or misfolded aggregates.