The cellular prion protein (PrPC) is a glycosylphosphatidylinositol (GPI)-anchored protein. We investigated whether PrPC can move from one cell to another cell in a cell model. Little PrPC transfer was detected when a PrPC expressing human neuroblastoma cell line was cultured with the human erythroleukemia cells IA lacking PrPC. Efficient transfer of PrPC was detected with the presence of phorbol 12-myristate 13-acetate, an activator of protein kinase C. Maximum PrPC transfer was observed when both donor and recipient cells were activated. Furthermore, PrPC transfer required the GPI anchor and direct cell to cell contact. However, intercellular protein transfer is not limited to PrPC, another GPI-anchored protein, CD90, also transfers from the donor cells to acceptor cells after cellular activation. Therefore, this transfer process is GPI-anchor and cellular activation dependent. These findings suggest that the intercellular transfer of GPI-anchored proteins is a regulated process, and may have implications for the pathogenesis of prion disease.