This in vitro study provides original data regarding the three-dimensional movements of the intervertebral foramen as the spine undergoes normal physiologic motions. Three-dimensional flexibility characteristics of fresh cadaver functional spinal units were determined. The same spinal units were fixed and thinly sectioned to yield quantitated anatomy of the soft and hard tissues of the specimen in three-dimensions. The flexibility and anatomic data were stored in a computer. A mathematical model was utilized to combine the two data sets, resulting in a precise three-dimensional description of the movements of the intervertebral foramen. Changes in foramen height, width, and area were obtained as functions of major spinal motions. Preliminary results indicate differences in intervertebral foramen kinematics of nondegenerated and degenerated spines. Such changes may affect the nerve root adversely and hence participate in pain production.