A growth factor has been purified to homogeneity from human pituitary glands. The pituitary growth factor (PGF) is trypsin-sensitive and acid- and heat-labile and has a molecular weight of 18,000 and an isoelectric point of 7.5. PGF was purified by heparin and copper affinity chromatography followed by carboxymethylcellulose 52. The amino-terminal amino acid sequence of PGF was established as PALPEXGGXGA and is identical with that of basic fibroblast growth factor at the identified amino acid residues. PGF was mitogenic for rabbit fetal chondrocytes and bovine corneal endothelial cells in the range of 0.015-15 ng mL-1. Heparin alone at low concentrations (0.5 microgram mL-1) was found to be weakly mitogenic for rabbit fetal chondrocytes. In combination with PGF a marked increase in cell growth was observed, which was inhibited by protamine sulfate. These data demonstrate the presence of a potent mitogen in human pituitaries that is structurally related to basic fibroblast growth factor and synergizes with heparin to promote cell growth.