The change in infrared dichroism with elongation has been observed at a series of temperatures for several infrared bands of ethylene-methacrylic acid copolymers and their salts. The orientation functions of hydrocarbon and meth­acrylic acid parts of the molecule were calculated as a function of the temperature of stretching. It is found that the orienta­tion function-strain coefficient for the un-ionized acid decreases uniformly with temperature, but that for the ionized salt passes through a maximum at about 40° where the strain-optical coefficient has been observed to pass through a maximum. Maxima are observed for the dichroism-strain coefficients for both the hydrocarbon and acid parts of the structure.