High‐intensity x radiation from the Stanford Synchrotron Radiation Laboratory storage ring has been used in a small‐angle scattering mode to study dynamic deformation behavior in polymers. Complete scattering curves were obtained as a function of time during relaxation with the strain direction oriented parallel and perpendicular to the plane of measurement. Interpretation is made of the resulting information on relative number, size, and time dependence of heterogeneities. A tentative model proposes that the application of stress starts a rapid creation of approximately uniform spherical voids which migrate and coalesce to form crazes and relieve the stress.