Two myeloma cell lines, MPC-11 and P3X63Ag8.653 (P3), have almost identical amounts of syndecan-1 at their cell surface. The syndecan-1 molecules from both lines are similar in size, have indistinguishable core proteins, and have similarly sized heparan sulfate chains. Nevertheless, syndecan-1 on MPC-11 mediates cell adhesion to type I collagen, whereas P3 cells do not bind collagen. Affinity co-electrophoresis reveals that intact syndecan-1 isolated from P3 cells binds collagen poorly and that syndecan-1 heparan sulfate isolated from MPC-11 has a 20-fold higher affinity for collagen than syndecan-1 heparan sulfate from P3. Analysis of disaccharide composition and oligosaccharide mapping also reveals differences between MPC- 11 and P3 heparan sulfate. Most notably, the level of N-sulfation and 2-O- sulfation is higher, and 6-O-sulfation lower, in syndecan-1 heparan sulfate from MPC-11 than from P3. Interestingly, levels of total sulfation of syndecan-1 heparan sulfate from MPC-11 and P3 are similar (75.6 and 72.6 sulfates/100 disaccharides, respectively), indicating that the difference in their affinity for collagen is not due to a difference in net charge. These data indicate that the fine structure of heparan sulfate can differ on identical proteoglycan core proteins, and these differences can control fundamental cellular properties such as cell-matrix adhesion.