A review of 105 consecutive cases of chymopapain chemonucleolysis for single level lumbar disc herniation was undertaken. Mean follow-up was 12.2 years (range 10-15.3). Patients were assessed using the Oswestry Disability Questionnaire. Eighty-seven patients were available for follow-up. An excellent or good response occurred in 58 patients (67%); four patients (4.5%) had a moderate response but were only minimally disabled. The treatment failed in 25 patients (28.5%) and 21 of these went on to surgery within a mean of 5.2 months (range 3 weeks-12 months). In 15 patients (71%) disc sequestration or lateral recess stenosis was found. Five of the remaining six cases had a large disc herniation at surgery. Surgery resulted in a significant improvement in nine cases. Discitis following chemonucleolysis occurred in six patients (5.7%). Chymopapain chemonucleolysis has a useful role in the management of lumbar intervertebral disc prolapse. However, its efficacy is dependent on careful clinical and radiological patient selection.