Simple micromechanical methods provide direct measurements of surface cohesion, elasticity, rigidity, and mutual attraction properties of surfactant double-layer membranes in aqueous media. Temperature-dependent tests yield explicit data for thermal phase transitions. Properties of mixtures of phospholipids (neutral and charged), cholesterol, and polypeptides have been studied. The results are essential for evaluation of theories of surfactant mixing, lamellar phase transitions, colloidal stabilization, and flocculation. © 1987 American Chemical Society.