To optimize the end-use properties of semicryst. polymers such as polyamide 11 (PA 11) in structures of interest for the petroleum industry, the modeling of their behavior under mech. load is a prerequisite. One way to perform this consists in describing the local material behavior by using a constitutive stress-strain equation and in calcg. the structural behavior with a finite element model. To evaluate these local deformations on a structural scale, simultaneous near-IR (NIR) spectroscopic and mech. measurements were performed in rheo-optical expts. From the corresponding data, conclusions were drawn in terms of the orientational behavior of the polymer in elongation-recovery tests up to 60% strain at 27 Deg and 60 Deg. Apart from the changes obsd. as a function of temp., significant spectroscopic differences could be detected for the absorption bands characteristic of aliph. sequences and the NH-functionalities, resp., of the investigated polymer.