A study of the applicability of secondary nucleation theory to the semirigid macromolecules poly(aryl ether ether ketone) (PEEK), poly(ethylene terephthalate) (PET), and poly(ethylene naphthalenate) (PEN) has been made. The main purpose of the study was to test the latest version of secondary nucleation theory, which permits the estimation of the lateral surface free energy fi om the characteristic ratio, C-proportional to. This was made through a numerical comparison of theoretical and experimental values of the products of the lateral and fold surface free energies sigma sigma(e). The surface free energy products were obtained from the direct application of the latest version of secondary nucleation theory to experimental data and compared to calculated values. Computation of the C-infinity values was made assuming that these macromolecules can be considered as polymeric chains with virtual bonds. Direct evaluations of the fold surface free energy sigma(e) used the well-known expression derived from secondary nucleation theory for the lamellar thickness as a function of supercooling. Other evaluations of sigma and sigma(e) were also made where possible, and they ranged from fundamental (Thomson-Gibbs) to empirical (Thomas-Stavely/Kaelble-Cirlin) methods. The product of surface free energies obtained from analysis of the experimental growth rates was always higher than the calculated values by a significant factor. Better numerical agreement was obtained if the data were analyzed assuming that only regime III was present. However, overall, it was concluded that the latest version of secondary nucleation theory does not quantitatively account for the crystallization behavior of this group of semirigid macromolecules.