The adsorption of N,N-diethyldodecanamide (DEDA) at the air-water interface has been determined at 24 degrees C by surface tension measurements. At monolayer saturation each molecule has a surface area, depending on the equation of state assumed, of about 41.2-45.6 Angstrom(2), comparable to that observed for sodium dodecyl sulfate and other somewhat similar surfactants, Micellization of DEDA appears not to occur below its aqueous saturation concentration of 1.4 x 10(-5) M. At saturation the surface tension is lowered to 37 dyn cm(-1), and the standard free energy of adsorption is about -46.5 kJ mol(-1). The surface adsorption deviates slightly from the Szyszkowski-Langmuir surface equation of state at coverages below 50%, and a two-state adsorption mechanism proposed by Lunkenheimer and Hirte appears to best account for this deviation.