Surgically removed discs from patients with either spondylolisthesis or tears of the posterior annulus fibrosus were analysed for water, proteoglycan, and collagen content and compared with post-mortem control material. Discs from patients with spondylolisthesis had a reduced proteoglycan content in all section sampled and less collagen in the outer annular layers. In contrast discs containing tears in the posterior annulus were unaltered biochemically, although extended studies on 2 patients indicated that there may be localised biochemical changes in the region of the tear itself. Collagen types I, II, and III and proteoglycan distributions were studies qualitatively by immunofluorescence. Collagen types I and III appeared to be reduced in discs from patients with spondylolisthesis, but again little change was found in patients with tears in the posterior annulus fibrosus.