The effect of a rigid plastic delordosating brace - the Flexaform brace - was studied in 48 patients with low back pain. In spondylolisthesis the brace gave pain relief in 13 cases, and the remaining two cases reported improvement. In seven cases with spinal stenosis, only two cases were free from pain, four were improved, and in one case the pain was unchanged. In 26 patients with chronic low back pain of unknown etiology, 17 cases did not improve, five cases improved and complete loss of pain was seen in only four cases. When all three groups were combined, a correlation was seen between pain relief in the brace and pain relief in the supine position and in the forward bending position.