The commercially available laccase from Myceliophthora thermophila was evaluated as catalyst for the polymerization of acrylamides. Using the so-called laccase mediator system (LMS), comprising laccase and beta-diketones, polymerization reactions can be performed using molecular oxygen as terminal electron acceptor. Thus, the LMS can substitute for diazo- or peroxocompounds as radical starters. Factors influencing the efficiency of the LMS, polymer properties, and the stability of the biocatalyst were investigated. Optimal reaction conditions were slightly acidic reaction media at elevated temperatures (around 50 degrees C). The enzyme is active and stable in the presence of high concentrations of water-soluble and water-insoluble cosolvents but is inactivated by acrylates. The average polymer weight can efficiently be controlled via the ratio of monomer to enzyme. The mediator (beta-diketone) concentration had no significant influence on the polymer properties. Laccase-catalyzed oxidation appears to be rate-limiting step of the overall reaction. The ambivalent role of molecular oxygen for reaction initiation as well as inhibitor of the polymerization reaction was investigated. Current limitations of the LMS are analyzed and an improved setup comprising physical separation of the enzymatic initiation reaction from the polymerization via immobilized enzymes is proposed. Thus, not only the biocatalyst is highly stabilized but also the product properties can be controlled.