In 10 patients with severe, chronic low back pain, we studied the effect of steroid and local anesthetic infiltration of anomalous lumbosacral articulations, formed between a transitional lumbosacral vertebra and the sacrum. There was immediate total relief of pain in 8 patients, and in 1 patient immediate partial relief that became total after approximately 7 days. Five patients subsequently relapsed to their former pain level in periods ranging from 1 day to 12 weeks, 3 patients continued to report adequate partial pain relief after periods of 7 to 41 months, and 1 patient remained free from pain 2 years after infiltration. IN some cases, infiltration of these articulations may be therapeutic, as well as diagnostic.