The propagation velocity of an ultrasonic shear wave can be used to detect anisotropic behavior in the mechanical properties of a solid. Thus, an ultrasonic shear transducer imbedded in an injection mold produces a signal that is sensitive to polymer orientation. This results in a non-invasive, on-line technique for monitoring the orientation of polymer in an injection mold cavity during part cooling and solidification. The technique is shown to be quite sensitive for semicrystalline polymers, but much less effective for amorphous polymers. Sensor results are compared to mechanical tests.