Bombardment-induced polymerization of meta-nitrobenzyl alcohol, widely used as a liquid solvent matrix in fast-atom bombardment mass spectrometry, produces an insoluble product presumably through any of several polymerization condensation reactions that involve expulsion of water. The product is insoluble in common organic solvents and in mNBA itself, and forms a brownish film on the surface of the liquid nitrobenzyl alcohol. Processes of oxidation and reduction of the alcohol may contribute to the formation of polymerized products.