Data of the melting point depression of isotactic polypropylene by n-alkanes (n(C) = 5-30) reported by Hamada and Nakajima are analyzed. Anomalous values of the enthalpy of fusion per chain repeat unit and the polymer-diluent interaction parameter that have been obtained by applying the Flory equation for the melting point depression of crystalline polymers are attributed to the effect of diluent on the morphology of polymer crystals. Information on the magnitude of this effect is obtained.