The development of anisotropy as a result of isothermal plastic deformation below the glass transition temperature is investigated for different deformation lempeiatures. Initially, i.wtropic polycarbonate was subjected to different extents of plastic strain in compression and the developed anisotropic wave .speeds were measured u.sing time of travel ultrasonic techniques. Longitudinal wave speeds were measured both in the axial and transverse direction of compression for different deformation temperatures. The wave moduli clearly indicated the development of a transversely elastic response as a result of uniaxial compression.