1. Cutaneous mechanoreceptor neurons were recorded in a preparation of isolated rat skin while the skin was stretched with an apparatus that allowed the parameters of tensile stress and strain to be controlled. 2. SA2 afferents were strongly directionally selective in response to stretch. Their responses were correlated most strongly with the tensile stress along the unit's preferred direction and were related poorly to strain variables. Threshold tensile stresses required to activate SA2s were low, on the order of 5 kPa. 3. C-mechanoreceptors were stretch activated. They lacked directional selectivity and had tensile stress thresholds similar to SA2s. 4. Hair afferents had only dynamic responses to stretch. SA1 afferents were not stretch activated.