An experimental model of disc herniation in tail discs of rats is described. Constant result on nucleus hernia and intervertebral narrowing were obtained by an easy manipulation on numerous rats. Intradiscal injection of aprotinin produced a widening of the disc height. Trypsin, collagenase, chymopapain, and hyaluronidase induced a narrowing of disc height; trypsin induced macroscopic necrosis of the soft surrounding tissues; and collagenase had a destructive effect on nucleus pulposus, annulus fibrosus, and even on end-plates. Chymopapain and hyaluronidase acted mainly on nucleus pulposus. Hyaluronidase could be of interest as a nucleolytic drug and needs further studies on optimal dosage and lack of side effects in the surrounding tissues before injecting it into human discs.