The processes of species specific cell cohesion and chemotaxis in differentiating cellular slime molds provide an advantageous system for the biochemical study of these nearly universal morphogenetic events. The carbohydrate binding proteins and their receptors are being characterized (from D. discoideum) in terms of covalent structure, conformation, topography, functional relationships and interaction with membrane lipid components. The chemotactic system employs cyclic AMP as an extracellular messenger. The cell surface receptor for cyclic AMP is being studied to characterize its binding properties, developmental regulation and mechanisms by which it is regulated on a rapid time scale. Solubilization and purification of the receptor is planned. Another component of this system, the extracellular and membrane bound phosphodiesterase is also being purified and characterized.