Curing reactions of certain laminates involve a series of chemical structure changes which occur with increasing temperature and/or pressure. This paper describes the use of a mid-infrared chalcogenide fiber to monitor the lamination of polymer prepregs in an autoclave. The fiber optic was used both as a wave guide and as a sensing element for acquiring evanescent wave spectra. The spectra were measured by embedding the fiber optic in a polymer prepreg package. The polymer prepregs studied include epoxy, polyimide, and bismaleimide triazine (BT) resins. The degree of cure and an understanding of the kinetic processes were obtained from the absorbance changes in specific bands. This in situ sampling technique demonstrates a new area of Fourier transform infrared (FTIR) spectroscopy for following the formation of polymeric bonds.