Dermatan sulfate (DS) is a component of connective tissue and catalyzes the heparin cofactor II-mediated inhibition of thrombin. Low-molecular-mass dermatan sulfates (LMMDS) are produced to prolong the antithrombotic activity of this substance. Cleavage of DS by nitrous acid leads to an LMMDS with a terminal 2,5-anhydrotalose (At) group at the reducing end which can react with primary amines. Tyramine (Tyr) was bound to the terminal At of LMMDS using reductive amination. LMMDS-tyr is produced using DS. LMMDS desacetglated were produced using totally deaminated DS. These compounds were employed as a model for the characterization of DS using NMR spectroscopy. The purity of the compounds was checked using capillary electrophoresis. The structure of the products was proven by 1H- and 13C-NMR spectroscopy. LMMDS-Tyr was radiolabeled with 125I for use in a radioimmunoassay. The anti-Xa activity and antithrombin activity of the tyramine-labeled DS are very low. The clotting assays Heptest, aPTT, thrombin time, and ecarin time indicate a highly anticoagulant-active substance. The heparin cofactor II-mediated inhibition of thrombin is similar to the parent compound. LMMDS were labeled "endpoint-attached." They are a new tool to understand the actions of DS in biologic systems.