The small proteoglycans fibromodulin and decorin may play an important role in regulating collagen fibrillogenesis and interactions with growth factors. Here, we describe the presence of these proteoglycans in cartilage submitted to different biomechanical forces. Fibromodulin from chicken and bovine articular cartilage was shown to self-associate. The different states of fibromodulin aggregation due to disulfide bonding demonstrable in different regions of the same joint suggest that the presence of different biomechanical forces results in the differential expression of small proteoglycans. A 250-kDa complex found in chicken tibiotarsal cartilage, which migrates as a 59-kDa component in SDS-PAGE under reducing conditions, and which was recognized by anti-fibromodulin antibodies, was not demonstrable in tarsometatarsal cartilage where a different fibromodulin complex has been recently demonstrated. Biglycan and decorin were not expressed in the same way in different regions of the bovine knee joint, suggesting that there is a relationship between the expression of small proteoglycans and the different biomechanical properties of a tissue.