Electron micrographs of tissue samples taken from the peripheral zones of bovine temporomandibular joint discs showed a preponderance of thicker collagen fibrils (mean diameter 97.6 +/- 18.9 nm), occupying a greater portion of the extracellular matrix (49.7 +/- 4.6%) and more closely spaced (mean fibril separation 38 +/- 7.2 nm) than fibrils from the centre of the disc (mean diameter 72.4 +/- 14.3 nm, proportion of matrix occupied 36.9 +/- 3.8% and mean fibril separation 43.7 +/- 6.5 nm). The cationic dye cuprolinic blue revealed numerous, thin, periodically aligned, glycosaminoglycan filaments on the surfaces of collagen fibrils from the periphery of the disc. In the centre of the disc thicker, 'leaf-like', glycosaminoglycan filaments were found lying between the fibrils. The differences in these ultrastructural features are believed to reflect the biochemical and biomechanical properties of the two zones.