Transforming growth factor (TGFs) are a family of peptide(s) defined by their ability to induce anchorage-independent growth of non-neoplastic indicator cells in soft agar. We found that acid-ethanol extracts of human anterior pituitary tissues were able to stimulate colony growth of normal rat kidney fibroblasts in soft agar. When subjected to gel-filtration on a column of Bio-Gel P-60 in 1 M acetic acid, the majority of TGF activity eluted in fractions corresponding to an apparent mol wt 15,000. The activity was heat- and acid-stable, but was inactivated by treatment with trypsin and dithiothreitol. Pituitary TGF-like materials did not compete with epidermal growth factor (EGF) for receptor binding and did not require EGF for colony-forming activity. Thus, human pituitary TGF was not like type alpha or type beta TGF.