The final step in the main pathway for the synthesis of GPI moieties in human cells is the addition of an ethanolamine phosphate to the third mannose residue of the glycolipid, donated by phosphatidylethanolamine. This reaction has been experimentally characterized in the mouse, where studies with mutated cell lines defective in GPI biosynthesis have established the role of two proteins, PIG-F and PIG-O, in this reaction (Hong et al. 2000). While a human PIG-F protein has been identified and shown to be involved in this event (Inoue et al. 1993), the human event has not been fully characterized and is therefore annotated here as inferred from studies of the mouse event.