Since 1981, we have studied a new therapeutic method of lumbar disc hernia using Nd-YAG laser. The purpose of this study is to establish easy, fast and safe method using laser for the improvement of chemonucleolysls and percutaneous nucleotomy. First, acute histological study for setting up an irradiating condition was performed using rabbits' and goats' lumbar disc. An optimum irradiating condition was decided by microscopic findings. And the time course of histological changes was studied with the optimum irradiating condition using rabbits' lumbar disc. The nucleus pulposus was vaporized and made a cavity just after the irradiation. And the healing process was very similar to that of conventional intradiscal nucleotomy. The proliferation of cartilage cell and fibrous tissue occurred and replaces the cavity.