We have identified and characterized an N-acetyl-galactosamine.4-O-sulfotransferase designated chondroitin-4-sulfotransferase-3 (C4ST-3) (GenBankTM accession number AY120869) based on its homology to HNK-1 sulfotransferase (HNK-1 ST). The cDNA predicts an open reading frame encoding a type II membrane protein of 341 amino acids with a 12-amino acid cytoplasmic domain and a 311-amino acid luminal domain containing a single potential N-linked glycosylation site. C4ST-3 has the greatest amino acid sequence identity when aligned with chondroitin.4.0-sulfotransferase 1 (C4ST-1) (45%) but also shows significant amino acid identity with chondroitin-4-O-sulfotransferase 2 (C4ST-2) (27%), dermatan-4-O-sulfotransferase 1 (29%), HNK-1 ST (26%), N-acetylgalactosamine-4-O-sulfotransferase 1 (26%), and N-acetylgalactosamine.4-O. sulfotransferase 2 (23%). C4ST-3 transfers sulfate to the C-4 hydroxyl of β1,4-1inked GalNAc that is substituted with a β-linked glucuronic acid at the C-3 hy. droxyl. The open reading frame of C4ST-3 is encoded by three exons located on human chromosome 3q21.3. Northern blot analysis reveals a single 2.1-kilobase transcript. C4ST-3 message is expressed in adult liver and at lower levels in adult kidney, lymph nodes, and fetal liver. Although C4ST-3 and C4ST.1 have similar specificities, the highly restricted pattern of expression seen for C4ST-3 Suggests that it has a different role than C4ST-1.