This study consists of (1) the extraction of proteoglycan from the human meniscus under dissociative conditions, (2) an investigation of the changes that occur in the abundance and structure of this proteoglycan with age and (3) a comparison of these findings with those for human articular-cartilage proteoglycan. Adult meniscus was found to possess proteoglycan molecules of similar size and glycosaminoglycan content to those present in cartilage, although tissue concentrations were considerably lower. In addition, age-related changes, with respect to the occurrence of keratan sulphate and the sulphation of chondroitin sulphate chains, were common to both tissues. The presence of aggregated proteoglycan was demonstrated, although specific interaction with hyaluronic acid was not conclusively shown biochemically. Differences were, however, noted in the structure of the proteoglycan between the two tissues: dermatan sulphate was found in the meniscus proteoglycan preparation and the core proteins exhibited some dissimilarities. A proteoglycan structure of this type would be compatible with its participation in meniscus elasticity, especially as the material is localized in a specific area.