Human growth hormone (hGH, somatotropin), a protein hormone from the anterior lobe of the pituitary gland, comprises a single polypeptide chain of 191aa residues. The 20kD variant form of human growth hormone (20kD hGH) presents in extracts from pituitary glands and it differs from the major form of hGH (22kD, 191aa) by the deletion of aa residues 32-46. The growth hormone amino acid sequence varies considerably between species, and non-primate growth hormones have little activity in man. Main functions of hGH and 20kD hGH are the stimulation of somatic and bone growth, as well as an increase in the size and mass of organs and tissues.