A series of hydrazones were prepared and tested for their ability to act as free-radical initiators for vinyl monomers. The most active initiators were the tertiary butyl hydrazones of aromatic, aliphatic ketones. The most reactive vinyl monomers were acrylate-type monomers, with methacrylate-type monomers being somewhat less reactive. When the most reactive hydrazone initiators, such as compound 1, were added to ambient-temperature solutions of acrylate monomers, such as aqueous sodium acrylate or aqueous acrylamide, polymerizations to hard gels occured within 1 min. In some cases of vinyl polymerizations, these hydrazone initiators can act as low-temperature alternatives to redox initiators.