The Lauritzen and Hoffman secondary nucleation theory was applied to linear growth rate data of syndiotactic polypropylene taken from the literature. Observation of the distinctive upward change of slope in plots of log G + U*/2.303R(T-c - T-infinity) versus 1/2.303 T-c(Delta T)f the regime II --> III transition at the crystallization temperature of 110 degrees C. Based on the input parameters judged to be the most accurate, the ratios of K-g,K-III/K-g,K-II were found to range from 1.7 to 2.2. Regardless of the crystal structure, if the growth is assumed to occur on the be plane, the lateral surface free energy, sigma = 11.3 erg cm(-2) and the fold surface free energy sigma(e) = 63.7 +/- 7.1 erg cm(-2) were found. The latter leads to the average work of chain folding of (q) over bar = 7.4 +/- 0.8 kcal mol(-1). If the growth is assumed to occur on the ac plane, the fold surface free energy is found to be sigma(e) = 82.4 +/- 9.1 erg cm(-2), while the lateral surface free energy is the same as previously noted. In this case, the work of chain folding of (q) over bar = 9.6 +/-1.1 kcal mol(-1) is found. These values are applicable to both regimes II and III. A detailed evaluation of the effects of changes in input parameters was also carried out.