A double blind study was carried out in 51 patients suffering from lumbar root compression syndrome of 12 days to 36 weeks duration. All patients had signs, symptoms and radiological abnormalities related to a herniated lumbar disc. Each patient received an extradural injection of either 2 ml (80 mg) methyl prednisolone or 2 ml normal saline solution. Neurological examination and interview of the patients with the aid of a questionnaire before and after extradural injection failed to demonstrate any statistically significant difference in outcome between the two groups. At follow-up 14 +/- 6 months after extradural injection 58.3 per cent of the patients in the control group and 51.9 per cent of the patients in the treatment group had undergone surgical treatment with laminectomy. Our results indicate that a single extradural injection of methyl prednisolone (80 mg) is no more effective than a placebo injection in relieving chronic symptoms due to myelographically demonstrable lumbar disc herniation.