The proton magnetic resonance absorption has been observed in several linear polyamides from 77°K to 400°K. The absorption line narrows gradually with increasing temperature up to about 280°K. A marked decrease in line width with increasing temperature occurs over a span of 20 or 30 degrees within the range of 280 to 400°K, and is presumed to result from the onset of rotation of chain segments. In a series of polyamides possessing an even number of carbon atoms between polar groups, this transition occurs at a lower temperature as the hydrocarbon portions are made longer (polydecamethylene octadecanediamide compared to polyhexamethylene adipamide). In the copolymer polyhexamethylene adipamide‐sebacamide, the transition region is at a lower temperature than in the pure adipamide or pure sebacamide. The x‐ray diffraction studies on polyamide fibers show that the chain packing becomes more symmetrical over these same temperatures. The resonance results are interpreted in terms of simple models.