Surface tension isotherms were recorded for mixtures of n-decyl-beta-D-glucopyranoside (Glu) and n-decyl-beta-D-maltopyranoside (Mal) and for the pure components. By use of conventional surface thermodynamics, the adsorbed amounts of Glu and Mal were calculated for different compositions and overall concentrations. The critical micelle concentrations (cmc's) of the pure components and the mixtures were between 2 and 2.2 mM. It was found that the molecule with the smaller headgroup, Glu, packs more tightly at the liqud-vapor interface at cmc, 37.5 Angstrom(2)/molecule as compared to 48.1 Angstrom(2)/molecule for Mal. The transition from a two-dimensional ideal solution state to a liquid-expanded state was investigated in detail. This transition occurs from an area/molecule of similar to450-550 to similar to150-200 Angstrom(2)/molecule and at very low values of the surface pressure, similar to1 mN/m. For a 1:1 mixture of Mal and Glu, an excess of the larger molecule, Mal, was found at the interface in a small concentration interval just after the ideal Henry's law region. At higher concentrations Glu adsorbs more readily, and at the cmc Glu occupies 73% of the interface. The observed adsorption behavior, surface pressure behavior, and the relative amounts of the two surfactants at the interface for the different mixtures are indicative of a hard disk behavior of the two sugar headgroups.