Intervertebral discs selected at random from autopsies and surgical operations on herniated discs were examined for evidence of amyloid deposition. Amyloid deposits were detected in 53 (81.5%) of 65 autopsy cases. Discs from subjects over 50 years of age revealed a significantly high incidence of amyloid deposition. Among herniated discs, amyloid deposits were documented in 49 (75.4%) of 65 surgical specimens. The incidence of amyloid deposition in intervertebral discs increased with advancing age. Intervertebral disc amyloidosis consisted of amyloid deposits of three morphological types: linear amyloid deposits around the degenerating chondrocytes (perichondrocyte type), and nodular or band-like deposits in the annulus fibrosus (annulus fibrosus type) and nucleus pulposus (nucleus pulposus type). We suspect that the precursor protein of perichondrocyte type amyloid is derived from chondrocytes, and those of annulus fibrosus type and nucleus pulposus types are derived from the blood. The amyloid deposits were resistant to treatment with potassium permanganate. Immunohistochemically, the amyloid deposits reacted with antibody against amyloid P-component, but not with antibodies against AA, A kappa, A lambda, transthyretin or beta 2-microglobulin. Ultrastructurally, the amyloid deposits were composed of 10 nm-wide nonbranching fibrils. The amyloid in herniated discs had the same biochemical and immunohistochemical properties as those found in autopsy cases. The immunohistochemical characteristics of the amyloid deposits suggest that it derives from an, as yet, unknown precursor protein.