Reversible addition-fragmentation chain transfer (RAFT) equilibrium constants, Keq, for the model system cyano-iso-propyl dithiobenzoate (CPDB) - cyano-iso-propyl radical (CIP) have been deduced via electron paramagnetic resonance (EPR) spectroscopy. The CIP species is produced by thermal decomposition of azobis-iso-butyronitrile (AIBN). In solution of toluene at 70 degrees C, Keq has been determined to be (9 +/- 1) L.mol(-1). Measurement of Keq kad/kb between 60 and 100 degrees C yields Delta E(a) = (-28 +/- 4) kJ.mol(-1) as the difference in the activation energies of k(ad) and k(beta). The data measured on the model system are indicative of fast fragmentation of the intermediate radical produced by addition of CIP to CPDB.