Because HA has an anti-inflammatory effect and prevents and/or reduces tissue adhesion, it was believed that HA epidurally-administered during epidural adhesiolysis procedures could alleviate the condition of patients with chronic lower back pain. For this reason, the following clinical trial evaluation of epidurally-administered HA neurotoxicity was performed by light microscopy (LM) and electron microscopy (EM) in rabbits. Twenty rabbits were randomly divided into two groups, a normal saline (NS) group (n = 10) and a HA group (n = 10). Saline (0.2 ml/kg of 0.9% solution) and the same volume of HA were injected into the epidural space. No rabbits showed any sensory-motor or