An experimental setup is described which allows simultaneous in situ measurements with the Kelvin probe and infrared reflection absorption spectroscopy (IRAS). Variations in the Volta potential were measured during corrosion of zinc surfaces in humid air, and information about the composition and the growth kinetics of the surface film was obtained by IRAS. The results show the Volta potential drops to between 2600 and 2700 mV/SHE after introduction of humid air due to activation of the zinc surface. With IRAS the growth of a surface film containing ZnO and Zn-5(OH)(8)Cl-2.H2O and zinc hydroxy carbonate was followed. With increasing thickness of the surface film the zinc surface is passivated and the Volta potential increases to between -100 and -200 mV/SHE after prolonged exposure. The results show that the experimental setup for simultaneous Kelvin probe and in situ IRAS measurements is a powerful tool for obtaining information about the changes in corrosion potential associated with the formation and growth of different types of corrosion products on metal surfaces.