This study has assessed the amounts of insulin-like growth factor I (IGF-I), fibroblast growth factor (FGF), transforming growth factor beta (TGF-beta), platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) and their binding to extracellular matrix components of Wharton's jelly. Studies were performed on the umbilical cords taken from human newborns delivered by healthy mothers. Wharton's jelly was separated and submitted to homogenisation and extraction with acetic acid and Tris-HCl buffer. The assays of growth factors were carried out with the use of ELISA commercial kits, together with SDS/polyacrylamide gel electrophoresis of tissue extracts followed by Western immunoblotting. Several growth factors, viz. acidic FGF, basic FGF, EGF, IGF-I, PDGF and TGF-beta were detected in Wharton's jelly. The amounts of these factors per gram of tissue vary from about 40 pg (EGF, PDGF) to about 200 ng (IGF-I). The amounts of peptide growth factors calculated per microgram of DNA are distinctly higher in Wharton's jelly in comparison to the umbilical cord artery. Western blot analysis demonstrated that almost the entire amount of these factors is bound to high molecular weight components. Since the number of cells in Wharton's jelly is very low and the amounts of extracellular matrix components are very high, it is concluded that the cells are strongly stimulated by peptide growth factors to produce large amounts of collagen and glycosaminoglycans.