In this study, virtually all sulfated glycosaminoglycan (GAG) synthesized and secreted by human synovial cells, both normal and rheumatoid, was detected in the form of proteoglycans of monomeric size. Enzyme hydrolysis studies that were performed demonstrated dermatan sulfate to be the dominant GAG in the proteoglycan, with lesser amounts of chondroitin 4/6 sulfate. Exposure to β-xyloside, used as a false “core protein,” resulted in marked enhancement of GAG chain formation, suggesting that the synthesis of the sulfated carbohydrate chain itself was not rate limiting. Proteoglycan synthesis and secretion were stimulated by several types of connective tissue activating peptides (CTAP); CTAP-III stimulation of incremental core protein and glycosaminoglycan was shown to be of a similar magnitude. Since chain synthesis was not rate limiting, it is suggested that stimulated proteoglycan formation caused by the CTAP peptides may be primarily modulated through increased formation of core protein.