Stephen Fried’s lab developed a mass spectrometry-based approach to probe protein folding on the proteome-scale. In this experiment, Philip To and coworkers unfolded and refolded E. coli extracts, probed the resulting proteins’ conformations using a permissive protease, and then used mass spec to sequence the fragments and compare to their original native forms. Their findings show that many proteins are incapable of fully refolding back to their native states following denaturation. This study lays the foundation to bring protein folding research into the ‘omics’ age.