Cultured smooth muscle cells from calf aorta utilize mevalonate as precursor to the synthesis of polyisoprenyl compounds of the dolichol family. In turn, the cell phosphorylates and glycoslates these prenols to yield polyprenylphosphoryl monosaccharides and polyprenylpyrophosphoryl oligosaccharides which proceed to serve as glycose donors towards the glycosylation of membrane glycoproteins. Formation of labeled prenyl saccharides is transient, which, as may be anticipated, is consistent with a labile intermediary role for these compounds in the carbohydration of complex proteins. A glycopeptide was isolated from the external surface of the cell whose carbohydrate portion bore great similarity in size, composition, and lectin binding properties to the prenol-associated oligosaccharide. Because of these similarities a precursor-product relationship may exit between the lipid saccharide and the cell surface glycopeptide. This relationship also was deduced from pulse-chase studies that were performed in the absence and presence of antibiotics and which demonstrated that protein synthesis inhibitors prevented the turnover of the polyisoprenylpyrophosphoryl saccharides and inhibited the appearance of the corresponding oligosaccharide moiety on the surface of the cell. Accumulation of prenyl saccharide intermediates in the intact cell did not occur, suggesting that their observed level in the presence of antibiotics may reflect their total cellular concentration and that their metabolically active pool may be at near maximal "oligosaccharide charge" at all times in the cell. Delineation of the metabolic origin and role of polyisoprenyl saccharides, localization of their sites of action, and definition of their control mechanisms may be fundamental to understanding the process of membrane glycoprotein and indeed membrane biogenesis. In addition, by sharing a common biosynthetic pathway with sterols, polyisoprenols may also be involved in events leading to atherogenesis so identified with the aortic smooth muscle cell.