Sixty patients with unilateral sciatica resulting from lumbar intervertebral disc hernlation were entered into a double-blind study. All patients had failed to respond to conservative management, and the diagnosis had been confirmed by metrizamide myelography. Following a randomized schedule, 30 patients had intradiscal injections of chymopapain, and 30 patients had intradiscal injections of an equivalent volume of normal saline solution. Two years after the injection, 77% of patients treated with chymopapain were assessed as moderately improved, compared with 47% of saline-injected patients. Fifty-seven percent of the chymopapain group were free of pain, compared with 23% in the saline group. Based on the late results of this study, chymopapain is recommended for the treatment of sciatica from intervertebral disc herniation when conservative measures have failed and before disc fragment excision is considered.