The following benzene derivatives have been pyrolyzed in a free radical mass spectrometer: benzene, toluene, benzaldehyde, anisole, diphenyl, phenyl ether, and benzyl ether. The products and intermediates were analyzed, particular attention being paid to the formation (and stability) of any aromatic free radicals found. The phenyl, benzyl, phenoxy, and benzoyl radicals, as well as atomic carbon, were detected. The first two could be obtained abundantly and are fairly stable below 1150°. The oxygenated radicals were much less abundant and appeared to be less stable.