The expression of the matrix protein chondromodulin-I has been studied in human intervertebral discs of 101 people using immunohistochemical analyses. The purpose of this report is to present data on the metabolic changes that were found to occur in the chondrocytes of intervertebral discs during development and aging. Chondromodulin-I was highly expressed during the gestational period and gradually decreased after maturation. It was detected in both the extracellular matrix and chondrocytes in the zone of hypertrophic cartilage, the zone of proliferative cartilage and the zone of resting cartilage in fetal discs. It was also present in the annulus fibrosus, nucleus pulposus and end-plate cartilage in mature discs. In degenerative discs, chondromodulin-1 immunoreactivity tended to be elevated in the remaining chondrocytes. Our findings suggest that the expression of the protein is developmentally regulated and upregulated through a defense mechanism against the degenerative processes of the aged intervertebral disc.