Abstract The sensory reinnervation of muscle spindles following lesions of the peripheral nerve was studied in hind limb muscles of the cat. Earlier results reporting complete redevelopment of both primary and secondary endings were confirmed. However, after section of the ventral roots reinnervation of muscle spindles was impaired in that many primary endings did not develop the spiral-like structures and their appearance remained abnormal for up to 120 days. The response to stretch in two-thirds of such de-efferented regenerated primary endings was also abnormal. Although the phasic and vibration responses were present, the slowly adapting part of the response to maintained stretch was defective or absent in many of the primary endings. From these results it appears that motor innervation of the muscle is important for the normal redevelopment of the complex structure and function of the primary ending of the muscle spindle during reinnervation. The results do not indicate whether de-efferentation causes a permanent impairment or only a delay in redevelopment.