The N-deacetylation and N-sulfation of N-acetylglucosamine residues in heparan sulfate and heparin initiate a set of biochemical reactions, which lead to the synthesis of oligosaccharide sequences that have specific ligand binding properties (1). These reactions are catalyzed by the monomeric enzymes GlcNAc Ndeacetylase/N-sulfotransferases (NDSTs), which have two catalytic activities (1). Multiple NDST isozymes have been identified, each having unique tissue distribution and enzymatic properties (2). Phylogenetic data suggests that NDST1-4 evolved from a common ancestral gene, which diverged to give rise to two subtypes, NDST1/2 and NDST3/4 (2). NDST1, which maps to human chromosome 5q32-q33.1, shares the most homology with NDST2, which maps to human chromosome 10q22 (3,4). The least conserved amino acids between these two enzymes are found in the N-terminus/putative transmembrane regions (3). The human NDST3 and NDST4 genes are closely linked on chromosome 4, mapping to chromosome 4q25-26 and 4q26-27, respectively (2,5,6). RT-PCR analysis of various mouse tissues reveals a restricted pattern of NDST3 and NDST4 mRNA expression when compared with that of NDST1 and NDST2, which are abundantly and ubiquitously expressed (2).