This paper reports results of studies of birefringence (&Dgr;) in ABS systems and in two component materials, measurements which reveal information about the orientation and response of these materials to deformation. Continuous measurements of (&Dgr;) at strain rates (&egr;˙) from 8.5×10−5to 3.3×10−3sec−1were carried out with a He&sngbnd;Ne laser light source on polystyrene (PS), poly(styrene‐acrylonitrile) (SAN), and two clear ABS polymers. Measurements at constant &egr;˙ were related to mechanical response of the materials in creep, and two tests for the invariance of the stress optical coefficient were developed. These were achieved through comparison of computer‐generated plots of appropriate rheo‐optic functions with rheological counterparts derived from previous creep measurements via the convolution procedure of Hopkins and Hamming. Such comparisons indicated nearly identical constant time dependences for the respective logarithmic plots of (&Dgr;/&egr;˙) and (stress/&egr;˙) vs time (t) for the PS and SAN polymers. Comparison of other functions confirmed the constant value of thestressoptical coefficient (SOC) implied above, |(SOC)| being 1.0×10−12cm2/dyn. This paper also presents results which indicate that the onset of yielding in the ABS systems can be studied by these optical techniques. It was observed that the increase in &Dgr; in the two ABS systems was followed by the onset of a high degree of scattering which produced a maximum (M) in each plot of apparent &Dgr; vst, the height ofMdecreasing with increasing &egr;˙. The relevance of this latter phenomenon to the study of impact strength and yielding in ABS systems is discussed.