The fine structural alterations in human lumbar spine ligaments were studied in tissue samples obtained from 8 young patients operated upon for idiopathic scoliosis and from 10 adult patients operated upon for herniated discs. The ultrastructure of the scoliotic ligaments was found to be normal. The majority of cells encountered were the fibroblastic-like cells. The collagen-proteoglycans interaction was similar to that described in other normal soft tissues. However, two forms of degenerative changes were demonstrated in posterior ligaments of patients with herniated discs. Metaplasia of ligamentous tissue into fibrocartilage was a common finding. The fibroblasts were replaced by chondrocytes. A few cells which had suffered necrosis were found. Alterations in the collagen-proteoglycans arrangement were also evidenced. This form of degeneration resembled that commonly associated with wear and tear phenomena. A second form of degeneration due to ageing was found to coexist with the aforementioned alterations.