There are many experiences and principles about posterior approach in the spine as surgical procedure in the treatment of the patients with low back pain. And the anterior approach to the disc with its excision and bone graft, less known to others, has become a relatively safe procedure with the increasing experience. The greatest advantage of anterior lumbar interbody fusion is that the reduction of lumbar vertebral slipping is possible, the distance between the involved bodies is well maintained and the rate of fusion increases by spreading the vertebral bodies and putting into the measured bone bloc especially in the patients with severe segmental instability or spondylolisthesis. We analysed 48 patients having anterior interbody fusion by using a specially designed reduction-spreader during eight years, from January 1.978 to December 1985. The results were as follows: 1. Among 48 cases, 20 cases were male and 28 cases were female; 12 cases were in the fourth decade and 19 cases were in the fifth decade-most common in the fifth decade. 2. 28 cases were at the level of L4–L5, 16 cases were L5–S1, and 4 cases were two levels(L3–L4 L4–L5 and L4–L5 LS–Sl). 3. Retroperitoneal approach was used for the L3–L4 and L4–L5, and transperitoneal approach was used for the L5–S1. 4. After distraction between the involved vertebral bodies using an effective device, reduction-sprea-der, a pair of full thickness iliac bone grafts were impacted into the interspace, maintaining the reduction after removal of the reduction-spreader. 5. Fusion was achieved between 3 months and 6 months in 46 cases except 2 cases. 6. Overall clinical results were as follows: good in 42 cases, fair in 6 cases. 7. The anterior interbody fusion using the reduction-spreader is found to be useful method in the treatment of low back pain with spinal instability diagnosed by lumbar flexion-extension lateral roentgenograms.