Osteoarthritis (OA) influences the levels of free intraarticular glucosaminoglycans (GAG). Little is known about the direction--decrease/increase--of these changes, and information on the correlation between GAG levels and the degree of OA is sparse. Objectives of this study were to investigate the correlation between intraarticular levels of sulphated and unsulphated GAG and the degree of experimental OA, the time course of these changes and whether GAG might be useful as a marker for OA. Twenty-one sheep were randomly assigned to three groups: (1) transsection of the posterolateral bundle of the anterior cruciate ligament, ACL (TD), (2) medial meniscectomy (ME), and (3) meniscectomy and resection of the ACL (MV). During follow-up clinical and radiological examinations were done. After screening for intraarticular effusions, a joint tab was performed and the levels of hyaluronic acid and chondroitin sulphate were measured. The radiological scores differ significantly between group TD and groups ME and MV (P < 0.01). Hyaluronic acid levels in ME and MV are significantly higher than in the controls. Significantly increased levels (P < 0.01) of chondroitin sulphate are found 6 months after ME and 1 year following TD. Clinical consequences: Hyaluronic acid levels--at least in the experimental setting--correspond to a certain degree with osteoarthrotic changes: increasing levels were found along with increasing postoperative interval and increasing grade of OA. Chondroitin sulphate, on the other hand seems, to lend itself as a marker for chondromalacia, in other words for prearthrotic deformities and early stages of OA.