Homogenized autogenous nucleus pulposus was injected into the lumbar epidural space of four dogs through an indwelling catheter. After daily injections of the material over 5 to 7 days, the dogs were killed at 5,7,14, or 21 days after the first injection. In four dogs that served as controls, normal saline was injected on an identical schedule and the dogs were killed at times identical to the experimental group. Evaluation of the dural sac, the spinal cord and its roots was performed by gross inspection and microscopic analysis. There was evidence of an inflammatory response to the nuclear material injected, but no inflammatory response occurred in the control group.