Heparin-binding growth factors I and II (HBGF) [1,2] (also known as acidic and basic fibroblast growth factors (FGF) are structurally related mitogens which stimulate growth or differentiation of a wide variety of cells of mesodermal or neuroectodermal origin. These two proteins belong to a family of growth factors and oncogenes which is currently known [3,4] to include:

• FGF-3 (int-2), induced by the integration of mouse mammary tumor virus (MMTV).
• FGF-4 (hst-1; KS3), a transforming protein independently isolated from a human stomach tumor (hst-1) and from Kaposi's sarcoma (KS3).
• FGF-5, an oncogene expressed in neonatal brain.
• FGF-6 (hst-2), a transforming protein that exhibits strong mitogenic and angiogenic properties.
• FGF-7 or keratinocyte growth factor (KGF), a paracrine effector of normal epithelial cell proliferation.
• FGF-8 or androgen-induced growth factor (AIGF).
• FGF-9 or glia-activating factor (GAF), a heparin-binding growth factor that may have a role in glial cell growth and differentiation during development.
• FGF-11 (FHF-3), FGF-12 (FHF-1), FGF-13 (FHF-2) and FGF-14 (FHF-4) [5], which seem to be involved in nervous system development and function.
• FGF-15, which may play an important role in regulating cell division and patterning within specific regions of the embryonic brain, spinal cord and sensory organs.
• FGF-16.
• FGF-17.
• FGF-18, which stimulates hepatic and intestinal proliferation.
• FGF-19,
• A FGF homolog of unknown function from Autographa californica nuclear polyhedrosis virus [6].

From the sequences of these related proteins, we have derived a signature pattern which includes one of the two conserved cysteine residues.