The three published randomized clinical trials of chymopapain injection vs. placebo injection for the treatment of herniated lumbar discs are reviewed. Despite some differences, the similarities in selection criteria, technique, and outcome assessment are great enough to justify pooling the results to obtain an overall assessment of chymopapain efficacy. These pooled results suggest that the odds of successful outcome (at least some improvement in symptoms after injection) are 2.6 times as great with chymopapain injection as those after placebo injection. This corresponds to a 50% greater probability of success with chymopapain than with placebo or a 23% increase in the number of patients successfully treated with chemonucleolysis over those successfully treated with placebo. The fact that data from 234 patients evaluated in randomized clinical trials could resolve a controversy over therapeutic efficacy that the uncontrolled evaluation of over 20,000 patients could not answer suggests that the current controversy over the relative efficacy of chymopapain and discectomy should be studied in the same way. The difficulties of such a study are discussed.