Melanotransferrin (MTf) is a membrane-bound transferrin (Tf) homologue foundparticularly inmelanoma cells. Apart frommembrane-boundMTf, a soluble formof themolecule (sMTf) has been identified in vitro [Food, ., Rothen-berger, S., Gabathuler, R., Haidl, ., Reid, G. & Jefferies, . (1994)J. Biol. , 3034–3040] and in vivo in Alzheimer’s disease. However, nothing is known about the functionof sMTf or its role inFeuptake.