A novel initiating system for free-radical polymerization at room temperature has recently been described by our laboratory. It is based on the catalytic properties of horseradish peroxidase (HRP) to generate radical species from hydrogen peroxide and 2,4-pentanedione (acetylacetone) through an oxydoreductive pathway. In the presence of an acrylic monomer (acrylamide), initiation takes place leading to a polymer. The enolic form of acetylacetone is assumed to directly intervene in the catalytic cycle so the question has been raised in order to determine if other β-diketones might play a similar role in HRP-mediated polymerization. Assumptions on the initiation mechanism are discussed in relation to the well-known HRP catalytic scheme.