Synthesis and degradation of intestinal mucosal and microvillous membrane glycoproteins were studied in control suckling rats, and suckling rats given cortisol acetate by intraperitoneal injection for 3 days. Cortisol acetate had no effect on total uptake of radioactive glucosamine by the protein free compartment of rat intestine. Early incorporation of [1-14C]glucosamine by intestinal glycoproteins was enhanced by cortisol, but stimulation was the same in membrane and homogenate fractions. Polyacrylamide gel electrophoresis of membrane proteins solubilized with 2% sodium dodecyl sulphate demonstrated a cortisol dependent change, characterized by loss of faster travelling glycoproteins, and a corresponding shift in maximum labelling at 3 h from these glycoproteins to more slowly migrating glycoproteins. Degradation was studied qualitatively with a double isotope technique. Glycoprotein degradative rates appeared to be stimulated by cortisol, but similarly in membrane and total homogenate fractions. On polyacrylamide gels, the areas occupied by glycoproteins with the highest apparent degradative rates, corresponded closely with the areas of most active labelling at 3 h. The rate of degradation in the most actively labelled zone appeared to be higher after cortisol than in the controls. The results indicate that cortisol does not alter membrane composition by inhibiting degradation of selected glycoproteins, and are consistent with a model in which cortisol stimulates the synthesis of specific membrane glycoproteins in suckling rats, while inhibiting synthesis of other glycoproteins.