We have previously reported changes in the chemical composition of cell surface membranes in diabetic rats (Chandramoulis, V. and Carter, Jr., J. R. (1975) Diabetes 24, 257-262 ). To examine the possible implications of these changes for cell surface structures, we have measured the binding of labeled lectins and desialylated glycoproteins to plasma membranes prepared from the livers of streptozotocin--diabetic and control rats. Lectins were chosen which have affinities for different carbohydrate moieties. The binding of ricin and concanavalin A to liver cell membranes from the diabetic rats was significantly reduced, but no change in the binding of wheat germ agglutinin was noted. Binding of desialylated thyrozine--binding globulin, previously shown to be dependent on membrane sialic acid residues, ws strongly suggest that insulin deficiency leads to generalized changes in cell surfaced glycoproteins, at least in this animal model of diabetes.