A randomized clinical trial of 30 patients with refractory lumbar disc disease with evidence of a herniation at a single intervertebral space on the myelogram is presented. Collagenase or a saline placebo was injected into the affected disc. Lack of pain reduction or lack of functional improvement was considered a therapeutic failure. Patients who failed to respond to the placebo could subsequently receive a collagenase injection. Thirty-three percent (33%) of the 15 patients who received a placebo and 80% of the 15 patients who received collagenase were rated successful 8 weeks after injection. The study demonstrates a statistically significant effectiveness of collagenase in the treatment of herniated lumbar disc disease.