Enzymes are environmentally friendly, non-toxic catalysts that have found many applications in synthetic polymer chem. However, until very recently no examples of enzyme-catalyzed, controlled radical polymns. were known. Here we review the nascent field of biocatalytic atom transfer radical polymn. (ATRP). The heme proteins horseradish peroxidase, Hb and catalase, as well as the copper-contg. enzyme laccase have been reported to display catalytic activity in activators regenerated by electron transfer (ARGET) ATRP of two model monomers, N-isopropylacrylamide and poly(ethylene glycol) Me ether acrylate. Bromine-terminated polymers, low polydispersity indexes, linear increase in mol. wt. with conversion as well as first-order kinetics indicate ATRP-type mechanisms. However, the first examples of biocatalytic ATRP also show that enzymes are much more complex catalysts than conventional ones.