Abstract: The chemoattractant cytokine CTACK activates and recruits cells expressing the receptor CCR10, is constitutively expressed in skin, is overexpressed in atopic dermatitis and psoriasis vulgaris, and may be involved in the preferential metastasis of melanoma to the skin. It bears little sequence homology to most members of the chemokine family and has an unusually long C-terminal tail. Neither the biochemical and biophysical parameters of its binding and signaling through CCR10 nor its binding to glycosaminoglycans (GAGs) have been described to date. In this work, I present a method for expression and purification of large quantities of CTACK, evidence about its oligomerization state in solution, and its molecular structure as determined by our collaborators at the University of Cambridge using nuclear magnetic resonance spectroscopy. Using truncation and point mutants, I define an epitope of CTACK involved in chemotactic activity. This epitope involves both canonical N-terminal residues and non-canonical residues at its C-terminus. Lastly, I define the GAG-binding epitope of CTACK and show that binding to GAGS induces massive aggregation of CTACK.