rbST is known by many names. These include “bST,” “bGH,” “rbGH”, “recombinant bovine growth hormone” and “Posilac.” The clinical name for the naturally occurring protein hormone produced in the pituitary glands of all cattle is “bovine somatotropin,” denoted as “bST.” Human beings have learned how to reproduce an exact copy of this substance by means of recombinant DNA technologies. This version of bST is called “recombinant bovine somatotropin” or “rbST.” These are the names scientists use to describe these substances.

All somatotropins – whether from cattle, dogs, monkeys or human beings – are growth hormones. bST and rbST are therefore sometimes referred to as “bovine growth hormone” (bGH) and “recombinant bovine growth hormone” (rbGH), respectively.

“Posilac” is a brand name, not a scientific title. It was trademarked by Monsanto Inc. to refer to the commercially available version of rbST that the company manufactures. Monsanto Inc. is the only company approved by the U.S. Food & Drug Administration (FDA) to manufacture and sell rbST within the United States.

from rBSTFacts.org