A series of step reaction polymers have been prepared and studied as melt films or in solution in the overtone region and the combination region of the near-IR. Systems containing aryl rings show bands in the 2.13- to 2.16-μm region which are not observed in those systems not having aryl rings. Polyester, polyamide, and urea-formaldehyde polymers show carbonyl, hydroxyl, and N[BOND]H overtones. Polyurethanes show only the intense band of N[BOND]H, in the 2.0- to 2.1-μm region. Ureaformaldehyde and polyamides show this same band. Relative band intensities were compared to the first overtone of C[BOND]H which appears at 1.67–1.72 μm. In this way, polymers can be compared in a quantitative manner, both with respect to reaction conditions and effect of heat curing.