We report the remarkable surface behavior of class II hydrophobin proteins HFBI and HFBII from Trichoderma reesei and the resulting effect that these proteins have on the stability of air bubbles to the process of disproportionation. The surface properties were studied using surface tensiometry and surface shear rheology. Surface tensiometry data show that hydrophobins are very surface active proteins, reducing the surface tension to approximately 30 mN m(-1). The rate at which the hydrophobins adsorb at the surface may also be related to the self-assembly behavior in aqueous solution. We further show that hydrophobins form air/water surfaces with high elasticity, the magnitude of which is well in excess of that of surface layers formed by other common proteins used as foam or emulsion stabilizers. The measured surface properties translate to the stability of bubbles with adsorbed hydrophobin, and in this study, we demonstrate the ability of hydrophobin to have a dramatic effect on the rate of disproportionation in some simple bubble dissolution studies.