It is shown that in order for the ''living'' radical polymerization me
diated by stable nitroxyl radical (SNR) to proceed successfully, a con
stant supply of initiating radicals (by, e.g., thermal initiation) to
make up for the loss of polymer radicals due to irreversible bimolecul
ar termination is essential in addition to the frequent reversible com
bination of polymer radical with SNR. The stationary rate of SNR-media
ted polymerization is totally independent of the SNR concentration, be
ing equal to the polymerization rate of the SNR-free system. Experimen
tal evidence is presented showing that in the ''living'' polymerizatio
n of styrene, both of these requirements are met in fact.