The lipocalins are a diverse, interesting, yet poorly understood family of proteins composed, in the main, of extracellular ligand-binding proteinsdisplaying high specificity for small hydrophobic molecules [<cite idref="PUB00005094"/>, <cite idref="PUB00000545"/>]. Functionsof these proteins include transport of nutrients, control of cell regulation, pheromone transport, cryptic colouration and the enzymatic synthesisof prostaglandins.<p> The crystal structures of several lipocalins have been solved and show a novel 8-stranded anti-parallel beta-barrel fold well conserved within thefamily. Sequence similarity within the family is at a much lower level andwould seem to be restricted to conserved disulphides and 3 motifs, whichform a juxtaposed cluster that may act as a common cell surface receptorsite [<cite idref="PUB00000545"/>]. By contrast, at the more variable end of the fold are found an internal ligand binding site and a putative surface for the formation of macromolecular complexes [<cite idref="PUB00003448"/>]. The anti-parallel beta-barrel fold is alsoexploited by the fatty acid-binding proteins (which function similarly bybinding small hydrophobic molecules), by avidin and the closely relatedmetalloprotease inhibitors, and by triabin. Similarity at the sequence level, however, is less obvious, being confined to a single short N-terminal motif.The lipocalin family can be subdivided into kernal and outlier sets. Thekernal lipocalins form the largest self consistent group, comprising the subfamily of beta-lactoglobulins. The outlier lipocalins form several smaller distinct subgroups: the OBPs, the von Ebner's gland proteins, alpha-1-acid glycoproteins, tick histamine binding proteins and the nitrophorins.</p> <p>Beta-lactoglobulin (Blg) is the major protein component of milk from a wide range of species but not human. Glycodelin or PP14 protein is the human equivalent of Blg and is secreted into the endometrium. Blg binds a wide variety of hydrophobic ligands but its function remains unknown. The crystalstructure of Blg has been solved [<cite idref="PUB00006131"/>], confirming membership of the lipocalinprotein family.</p> Beta-lactoglobulin