Tetranectin is a recently discovered plasminogen binding protein from human plasma, with a known primary structure. Its interactions with various sulphated polysaccharides and trypan blue has been investigated by crossed immunoelectrophoresis, immunosorbent assay (ELISA) and gel filtration experiments. Interaction of tetranectin with chondroitin sulphate A, B, and C, heparan sulphate and trypan blue could be demonstrated by crossed immunoelectrophoresis against monospecific rabbit anti-tetranectin. Interaction of tetranectin with fucoidan could be demonstrated by all three methods, and this interaction could be prevented by heparin and to a lesser degree by chondroitin sulphate A and C, but not by fucose. These findings, together with the recently published findings, that tetranectin is present in exocrine and endocrine glands as well as in secreting surface epithelia and mesenchyme, suggest that tetranectin, in conjunction with proteoglycans, may have a function in the packaging of granules or as a participant in exocytocic processes.