First, we report the development of Fourier transform infrared (FTIR) spectroscopic methods to determine the alpha/gamma -crystalline phase ratio of polyamide-6 fibers and, in combination with density measurements, the total crystallinity. Using density determinations of the crystallinity of pure alpha and pure gamma samples, we found the absorption coefficient ratio for the 930 (alpha) and 973 cm(-1) (gamma) bands to be 4.4, from which we could obtain the alpha/gamma ratio for any polyamide-6 sample. The application of this FTIR method to the quantitative analysis of phase changes during thermal treatment and the drawing of polyamide-g was then made. We confirmed that crystallization during thermal treatments involved increases in both phases and did not involve crystal-to-crystal transformation, whereas drawing involved both crystallization of the amorphous phase in the cu form and gamma --> alpha transformation. Finally, we revisited the band assignments for the amorphous phase of polyamide-6 and found that the band at 1170 cm(-1) was not an amorphous band but, because its absorbance was independent of crystallinity, could be used as an internal reference band. The band at 1124 cm(-1) was reliably attributed to the amorphous phase. (C) 2001 John Wiley & Sons, Inc.