At 35.7% the average rate of pseudarthrosis following ventral spondylodesis of a segment of the lumbar spine is very high. The inadequate degree of primary stability in the segment to be ankylosed is seen as the fundamental reason for this. In the present paper an implant made of a nickel-titanium alloy ("Memory Alloy") is described, which is inserted intercorporeally and immobilizes the moving segment by traction. Experiments in sheep have confirmed that the anchorages of the implant are stable; it was also established that bony fusion occurred both around the implant as well as through it. Observations thus far in 10 patients treated by this method have shown that the implant remains stably anchored, and in some cases clear signs of bone bridge formation were demonstrable on radiographs after only a short time. If the primary stability provided by the Memory implant continues to be thus confirmed, postoperative hospitalization will in future be limited to a few days.