The activity, Phi, of AgBr, AgI, PbF2, Ag2S, LiF, and CaF2 in the catalyzed nucleation of poly(ethylene terephthalate) (PET) melts was determined using a nonisothermal differential scanning calorimetry (DSC) technique. A comparison with existing experimental data was made. It is established that the higher the melting temperature of the substrate the lower its activity as a crystallization core in the heterogeneous nucleation of PET. The lateral surface energy, sigma, the end surface energy, sigma(e), the adhesion energy, beta, and the difference between the surface energies at the substrate/melt, sigma(sf), substrate/deposit, sigma*, and the total energy of misfit dislocations, E(d) [i.e., sigma(sf) - (sigma* - E(d))] were calculated.