Hexabrachion (Tenascin) is a large glycoprotein that appears in extracellular matrices as a disulfide-linked multimer. It is synthesized in an ordered fashion at particular sites during development, is made in large amounts by certain tumors, and is found in restricted tissue locations in the adult. In this report, we describe the sequence of a full length cDNA of human hexabrachion. The encoded protein contains a total of 2203 amino acids and is a linear array of discrete reiterated domains. At the 5' end are encoded hydrophobic residues and 8 flanking cysteines predicted to be responsible for assembly of hexabrachion polypeptides into a radially arranged, six-armed complex. Following this region are 14 1/2 contiguous 31-amino acid epidermal growth factor-like repeats that have a unique structure with respect to the known examples of this type of domain. Immediately adjacent to these repeats lie 15 uninterrupted segments of approximately 90 amino acids which are similar to the Type III units found in fibronectin. At the carboxyl terminus of the protein is a 210-amino acid domain that is similar to fibrinogen. The domain structure of this protein is consistent with the potential for interaction with multiple ligands and for roles in cell adhesion and/or signaling.