Nucleating agents with an approximate to6.5 Angstrom lattice parameter induced the a phase of isotactic polypropylene (iPP, alpha-iPP). A 6.5 Angstrom periodicity is also involved in the nucleating agents for the beta phase of iPP (beta-iPP). The similarity in substrate periodicities suggests that some nucleating agents may induce either the alpha or beta phase under different crystallization conditions. 4-Fluorobenzoic acid, dicyclohexylterephthalamide, and gamma-quinacridone (the latter two are known as beta-iPP nucleators) were tested over a wide range of crystallization temperatures [up to crystallization temperature (T-c) > 145 degreesC]. The two former nucleating agents induce exclusively alpha-iPP and beta-iPP, respectively. gamma-Quinacridone on the contrary is a versatile agent with respect to the crystal phase generated. More specifically, the same crystal face of gamma-quinacridone induces either beta-iPP or alpha-iPP when T-c is below or above 140 degreesC.