In order to determine the intracellular location of heparan N-deacetylase/N-sulphotransferase, cDNAs encoding human heparan glucosaminyl N-deacetylase/N-sulphotransferase were cloned from human umbilical vein endothelial cells. The deduced amino acid sequence was identical to that of the human heparan N-sulphotransferase cloned previously [Dixon, Loftus, Gladwin, Scambler, Wasmuth and Dixon (1995) Genomics 26, 239-244]. RNA blot analysis indicated that two heparan N-sulphotransferase transcripts of approx. 8.5 and 4 kb were produced in all tissues. Expression was most abundant in heart, liver and pancreas. A cDNA encoding a Flag-tagged human heparan N-sulphotransferase (where Flag is an epitope with the sequence DYKDDDDK) was transfected into mouse LTA cells. Immunofluorescence detection using anti-Flag monoclonal antibodies demonstrated that the enzyme was localized to the trans-Golgi network. A truncated Flag-tagged heparan N-sulphotransferase was also retained in the Golgi, indicating that, as for many other Golgi enzymes, the N-terminal region of heparan N-sulphotransferase is sufficient for retention in the Golgi apparatus.