A method based on Fourier transform infrared (FTIR) transmission spectra is proposed to measure the crystallinity of isotactic polypropylene (iPP) samples. The method parameters were tuned as compared with wide-angle X-ray scattering measurements performed on test samples characterized by different crystallinity values obtained by solidification of thin iPP films under several cooling rates in a homemade device. The FTIR dichroic ratio measurements were adopted to measure crystalline and average Hermans' orientation factors of iPP samples obtained by film casting. The crystalline orientation measurement method was validated as compared with the birefringence measurement. The techniques were successfully used in real time during some film-casting runs with a suitably modified FTIR system made of a spectrometer equipped with two optical guidelines and an external detector. Real-time measurements are reported and discussed. (C) 2003 Wiley Periodicals, Inc.