Insect vitellin in ovary acts as a storage protein for formation of new organs during embryogenesis. Vitellogenin, the precursor of vitellin, is the protein which is synthesized by Int body, released into the haemolymph, and via receptor mediated endocytosis, taken up by the growing ovary to become vitellin. Most of the insect vitellogenin is cleaved in the fat body and the specific cleavage site is recognized by the endopeptidase. Because of its female specificity, vitellogenin can be identified by electrophoresis. The analysis of amino acid sequences can make a molecular phylogenetic tree of insect species. Because of differences in nutritional needs of different animals, the analysis of amino acids composition of vitellogenin can lead to understand the function of vitellogenin. The specific vitellogenin receptors in oocyte membrane are identified by culturing ovaries with vitellogenin and ligand blotting. Insect vitellogenin receptors show high affinity to vitellogenins. Storage protein and lipophorin in larval haemolymph react immunologically with ovary extracts of the same species indicating that these proteins are present in ovary. But vitellin does not react with storage protein and lipophorin. As a complex protein, vitellogenin molecule can be a good model to study processing because it changes in subunit structure.