In a model culture system hyaluronan has been shown to promote cell ruffling and random cell locomotion. At the same time it promotes both protein tyrosine phosphorylation and phospholipid breakdown. These results indicate that this glycosaminoglycan, in addition to its previously described role as a regulator of adhesion and cytoskeletal organization, may also influence cell behaviour via second messenger formation. A cell-associated hyaluronan-binding protein (cell-HABP) has been isolated from locomoting fibroblasts that may represent one binding site that transduces these effects of hyaluronan. This protein is concentrated in the lamellae and ruffles of migrating fibroblasts but is lost from the cell surface as cell locomotion slows. It is a large (molecular mass estimated at 1-2 x 10(6) daltons) complex of proteins that includes a hyaluronan-binding site and a protein kinase. The protein kinase is responsive to hyaluronan and is related, antigenically, to the pp60src protein kinase. The function of cell-HABP has not been characterized but its location, regulated distribution and enzyme characteristics suggest that it may be involved in hyaluronan-regulated cell locomotion.