Pituitary extracts of human growth hormone have been used extensively for therapy of growth hormone deficiency, although they are known to contain a variety of contaminating polypeptides. Biosynthetic human growth hormone is now available for this use and appears to be functionally identical in promoting growth. To establish additional criteria of identity we compared the effect of these two hormone preparations on a family of hepatic messenger RNA sequences in hypophysectomized adult male rats. Total hepatic RNA from these animals was translated in a cell-free rabbit reticulocyte lysate. Five translational products previously demonstrated to be responsive to ovine and methionyl-human growth hormone were found to be equally induced by pituitary derived human growth hormone, despite demonstrable heterogeneity in pituitary derived preparations. In addition, no significant alterations in approximately 200 non-growth hormone responsive translational products were identified. Methionyl and pituitary derived growth hormone have identical effects on the expression of hepatic mRNA.