Experimental data have been obtained on the stress‐relaxation modulusEr(t) of several copolymers in their transition regions. The new data are expressed as master curves which can be fitted to the Gauss Error Integral form of reduced equation, as previously proposed. It appears possible to characterize the time and temperature‐dependence ofErof amorphous polymers in general by means of the parameters of this equation:E1(glassy‐state modulus),E2(rubbery‐state modulus),Td(distinctive temperature, related to second‐order transition temperature),Kd(characteristic relaxation time atTd), andh(parameter related to steepness of master curve). In the butadiene‐styrene series, the effect of composition on these parameters has been determined.