Ag-NPA-1 (AgFABP), a 15 kDa lipid binding protein (LBP) fromAscari-dia galli, is a member of the nematode polyprotein allergen/antigen (NPA) family. Spectroscopic analysis shows that Ag-NPA-1 is a highly ordered, a-helical protein and that ligand binding slightly increases the ordered sec-ondary structure content. The conserved, single Trp residue (Trp17) and three Tyr residues determine the fluorescence properties of Ag-NPA-1.