The neonatal Fc receptor (FcRn) is a major histocompatibility complex class I-related molecule that regulates the half-life of IgG and albumin. In addition, FcRn directs the transport of IgG across both mucosal epithe-lium and placenta and also enhances phagocytosis in neutrophils. This new knowledge gives incentives for the design of IgG and albumin-based diag-nostics and therapeutics.