The term connective tissue growth factor (CTGF) was first used in 1991 to describe a mitogenic and chemotactic factor for fibroblasts that was produced by human umbilical vein endothelial cells (HUVECs) in vitro [1], The primary translational products of both human CTGF (hCTGF) and porcine CTGF (pCTGF) are predicted to comprise 349 residues, the first 26 of which are a presumptive signal peptide [1,2]. Mouse CTGF (mCTGF; also termed fisp-12 or βIG-M2) is predicted to comprise 348 residues, of which the first 25 are a hydrophobic signal peptide [3,4]. Secreted forms of CTGF from all three species are thus predicted to comprise 323 residues, 38 of which are conserved cysteine residues. Metabolic labeling and immunoprecipitation studies of cell lysates and conditioned medium have shown that CTGF proteins of approximately 38 kDa are produced and secreted in various cell cultures [2,5,6]. CTGF, which is encoded by a transforming growth factor-β (TGFβ)-inducible immediate early gene [3], has been strongly implicated in a variety of fibrotic disorders [7—11], wound healing [12-14], embryonic development [5], and uterine function [2,15]. Although the 38-kDa form of CTGF was initially implicated in many of these processes, low-mass forms of CTGF of Mr 10,000-20,000 have since been discovered in uterine secretory fluids [15] and fibroblast conditioned medium [6].