This week's issue of PNAS focuses on mass spectrometry and "attempts to illustrate the breadth and uniqueness of applications of molecular MS to a variety of scientific fields with current examples." Matthias Mann and Neil Kelleher write about how the latest generation of mass spectrometers has helped proteomics come of age and how precision proteomics is now possible. One paper reports on using DESI-MS imaging to see the distribution of clozapine, an antipsychotic drug, and its metabolite in brain, lung, kidney, and testis samples. In another, Vanderbilt researchers used imaging MS to look at Aβ isoform distributions in Alzheimer's plaque samples, mouse brain protein maps, and protein distribution in breast carcinoma. Other papers cover petroleomics, detecting extraterrestrial aromatic molecules, nanocalorimetry, among other topics.