Rat lung alveolar surfaces and contents were studied after using concanavalin A as a bifunctional agent to link exposed sugars to horseradish peroxidase, in accordance with a technique developed by Bernhard and Avrameas ('71). The Graham and Karnovsky ('69) diaminobenzidine procedure then was used to provide and electron-dense reaction product so as to define the distribution of complex carbohydrates in alveoli. A layer of very dense raction product was intimately associated with the outer leaflets of the luminal plasma membranes of type I and II pneumocytes. Masses of generally less dense reaction product extended irregularly into the alveolar coated by reaction product. When highly ordered tubular myelin bodies were seen, the reaction product filled all the "gutters" created by the intersentions of the membranes. Reasons are presented for believing that the intrinsic periodicity of the tubular myelin may be created and maintained by the domains ol technique. The distribution of autologous albumin, demonstrated by antibody staining by Bignon et al. ('75), apparently coincides with the carbohydrate pattern, suggesting both may be associated as a glycoprotein. The ultimate relationships between carbohydrate moieties and phospholipid membrane systems proved to be of such complexity that we believe it justifiable to think that they also may be truly complexed together.