Three sulphated polysaccharides labelled at the reducing end with three different chemical treatments (2-aminopyridine (2-AP), 8-amino-1,3,6-trisulphonic acid (ANTS) and 6-(biotinyl)-aminocaproyl-hydrazide (BACH)) were compared. Molecular weight, chemical composition, nuclear magnetic resonance features and anticoagulant activity expressed as activated partial thromboplastin time were studied to determine whether structural and biological properties were retained or not after labelling. Partial depolymerisation and reduced biological activity were observed when reductive amination was performed with 2-AP. The initial properties were better retained with ANTS, and BACH did not modify the anticoagulant and structural properties. (C) 2002 Elsevier Science Ltd. All rights reserved.