For the first time, electron paramagnetic resonance spectroscopy was used to compare numbers and distributions of radicals produced in frontal free-radical polymerization of multifunctional acrylates and methacrylates to those produced by bulk free-radical polymerization. A comparison of radical concentrations was performed for individual polymers and selected copolymers of trimethylolpropane trimethacrylate (TMPTMA), 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate (PETA). Frontally polymerized samples showed a large spike in intensity at the point of initiation. Within a few centimeters, the radical signal diminished to a steady state. The radical concentration remained almost constant over 3 months under helium in flame-sealed tubes. The types of radicals were similar to those in bulk polymerization. For both TMPTMA and PETA, frontally polymerized samples had significantly higher numbers of radicals than did the bulk-prepared samples, achieving concentrations as high as 8.7 x 10(-3) mol/kg in the frontally prepared samples of TMPTMA. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4261-4266, 2011