Bisdermican (PG760) is a large, heterodimeric, dermatan sulfate proteoglycan found in selected basement membranes, smooth muscle cell layers, and different extracellular matrices. Age-dependent and developmentally regulated alterations in glycosaminoglycan structure and quantity have been shown to be functionally relevant for a number of physiological and pathological processes. Bisdermican was purified from human skin fibroblast cultures of different age and confluency. Following beta-elimination, glycosaminoglycan chains were analyzed by Sephacryl-S-300 chromatography. Glycosaminoglycan chains of Bisdermican from infantile fibroblasts had a molecular weight of 19 kDa, whereas the glycosaminoglycan chain of the large Bisdermican subunit purified from confluent fetal fibroblast secretions was slightly larger (Mr = 24 kDa). Bisdermican derived from subconfluent cultures of fetal fibroblasts displayed the largest glycosaminoglycan chains with a molecular weight of 31.5 kDa for the large subunit, and a molecular weight of 22 kDa for the small subunit. Thus, Bisdermican displays a molecular polymorphism that is related to its chronological age and proliferative state.