The most reliable tendon reflex is the patellar reflex, which is mediated by the femoral nerve through spinal cord segments L4-L7. With the limb held in partial flexion, the clinician should elicit this reflex by lightly tapping the patellar tendon with a plexor or pediatric hammer. This reflex should be tested with the pet in both lateral recumbencies. For inexplicable reasons, this reflex commonly is elicited more easily in the limb adjacent to the floor. It is noteworthy that one or both patellar reflexes may be absent in older dogs with no other neurologic signs.4 Responses are typically graded as absent (0), hyporeflexive (+1), normal (+2), hyperreflexive (+3), or clonic (+4). An absent or hyporeflexive reflex occurs when there is a disease of a portion of the reflex arc (most commonly in the LMN unit). Hyperreflexia or clonus may be present in UMN diseases.