The plasma membrane contains both glycoprotein and glycolipid. The structural diversity of these macromolecules suggests a role in information transfer between a cell and its environment or between two cells; for example, surface carbohydrate probably plays a role in differentiation. A pilot project was undertaken to study glycoprotein and glycolipid metabolism in spermatogenesis; the latter process was chosen because it is an excellent model for differentiation and because it was hoped that information might be obtained relevant to reproductive physiology. The pilot project indicated that a full-scale investigation was warranted, as follows: (1) Glycoprotein metabolism: The germinal cells of the mouse testis can be separated into partially purified cell fractions by sedimentation in a Ficoll gradient. Three glycoprotein glycosyltransferases have been measured in these cell fractions and it has been shown that glycoprotein synthesis is maximal at the 1 degree and 2 degrees spermatocyte stages but becomes negligible in the spermatozoal stages. These studies have been extended to two sterile mouse mutant strains; it is hoped to study other mouse strains as well as normal hypophysectomized and cryptorchid rats. We also plan to study glycoprotein synthesis by injection of radioactive precursors such as glucosamine and following incorporation into glycoprotein by electrophoresis and by radioautography of testis sections. (2) Glycolipid metabolism: a preliminary survey of testis glycolipids showed the presence in the testes of several mammalian species of a testis-specific glycolipid, 1-O-alkyl-2-O-acyl-glyceryl- 3-Beta-D- galactopyranoside- sulfate. Study of newborn rats with immature testes and of a sterile mouse mutant strain indicates localization of this glycolipid to the germinal cells. Proof of this localization will be attempted by radioautography of testis sections following labeling of the lipid with S-35 sulfate. Testis homogenates and subfractions will be studied in a search for the following three enzymes required for synthesis of the glycolipid: acyl transferase, galactosyl transferase and sulfotransferase. The roles of these enzymes in spermatogenesis will be studied.