A new ambient ionization technique could turn mass spectrometry into a common surgical tool by enabling the collection of mass spectra of tissue samples in real time during surgery. Such a capability would be particularly advantageous for distinguishing cancerous from healthy tissue. Zoltán Takáts of Justus Liebig University, in Giessen, Germany, and coworkers developed the technique, called rapid evaporative ionization mass spectrometry, in which an electrosurgical electrode heats and evaporates tissue that is transferred to a mass spectrometer (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200902546). Each measurement takes only a fraction of a second, so the method provides analysis of the tissue while it is being cut. Because different tissues harbor different compositions of biomarkers, such as phospholipids, the researchers were able to create a tissue identification system using a spectral library and principal component analysis. When they tested the system in a canine melanoma model, they were able to distinguish healthy epithelial tissue from melanoma tissue and from cancerous lymph nodes.