The characteristic of angular changes of lumbar spinal motion segments in 28 normal male volunteers was evaluated. The subjects were kept lying at supine position on X-ray table, and both of their hip joints were flexed passively from neutral to 90 degree flexion with interval of 30 degrees. The angular variables were measured from the left lateral view X-ray film of lumbar spine. We drew the following interpretations from the analysis of variables with anatomical considerations.

1) The evaluation of 7 angular variables in comparative way by testing their mean ranks at each of the 4 hip positions appeared to be diagnostically valuable with significant concordance of the ranks among 28 subjects(p-value<0.05).

2) The Intervertebral Disc Angle(IDA) of L4-L5 and L5-S1 had the smallest inter- subject variations with significantly constant decrement according to the hip flexion (p-value<0.05), showing that they were diagnostically the most adequate variables for angular analysis at this kind of study.

3) If the minimal lumbar lordosis at supine is required for treatment, the 60 degrees of passive bilateral hip flexion would be the best for it.

4) The motion segment of L4-L5 and L5-S1 showed the maximal motion in concordance with the other studies practiced in standing position, but the L1-L2 had the third largest motion on the contrary to the other workers who have insisted its minimal motion among lumbar spine motion segments. This discrepancy seems to be caused partly by dramatic decrement of external supporting power for lumbar spine from paraspinal and psoas muscles when the subject's position changed from standing to supine, and by the minimal diameter of the psoas muscle at L1-L2 level.