A series of isotactic polypropylenes were investigated to account for total defect content using xylene fractionation and carbon-13 NMR experimental methods. The defects of interest were percent atactic content, copolymer content, and configurational defects. Experimental equilibrium melting temperatures were obtained for each material using the Gibbs-Thomson equation and extrapolation to infinite crystal thickness or the Hoffman-Weeks analysis. The experimental equilibrium melting temperature was then compared with the theoretical equilibrium melting temperature predicted by Flory's melting point depression model. Flory's model was found to fit the experimental data using an equilibrium melting temperature of 186 degreesC when configurational defects are ignored. However, to account for all defects, the equilibrium melting temperature for 100% isotactic polypropylene must be increased from 186 to 192 degreesC.