The aim of this study was to develop a method to identify cows illegally treated with bovine somatotropin (BST). Using the Western ligand blotting technique, BST treatment was shown to cause a dramatic decrease of IGF‐BP‐2 in the serum of treated cows. Measurement of the insulin‐like growth factor‐binding protein‐2 (IGF‐BP‐2) concentration in cow plasma could thus be a good way to identify BST‐treated animals. In order to develop an immunoassay specific for bovine IGF‐BP‐2, polyclonal antibodies against synthetic peptides of bovine IGF‐BP‐2 were produced. Three peptides were chosen in the [150–190] region of the molecule, which display no identity with other IGF‐BPs in serum: [154–165], [171–184] and [163–176]. Two antisera were obtained which reacted specifically with the entire bovine IGF‐BP‐2 molecule, both of which came from rabbits immunized with the [163–176] peptide.