Electrophoretic analysis of the proteins synthesized by cultured human skin fibroblasts demonstrated that the major component released into the medium is a high molecular weight fucosylated glycoprotein (MFGP). Gel filtration chromatography under denaturing and reducing conditions indicated that MFGP has a molecular weight of approx. 250,000; but appears to behave as a disulphide-linked dimer when unreduced. MFGP is further distinguished as the major labelled macromolecule in the medium after incubation of fibroblasts with [35S]cysteine. The role of this glycoprotein is unknown but it bears a striking resemblance to a presumptive structural glycoprotein recently shown to be secreted by arterial smooth muscle cells in culture, and may also be related to a group of much studied cell surface glycoproteins.