Polymerization of vinylcarbazole by free-radical initiators, especially azobisisobutyronitrile, yields polymer of higher molecular weight and better appearance than can be made by thermal polymerization. The polymerization is retarded and the molecular weight of the polymer lowered by amounts of anthracene comparable to or somewhat larger than the initiator concentration, but these effects soon show saturation at higher anthracene concentrations. Phenanthrene has a slight inhibiting effect which increases with concentration, the polymerization being almost completely inhibited at very high phenanthrene concentrations. The results are discussed in terms of the formation of an intermediate complex between the aromatic hydrocarbon and the growing polymer chain.