The growth kinetics of passive films on Fe, Fe-10, Ni, Fe-10 Cr, Fe-10 Ni-10 Cr have been determined in pH 8·4 borate buffer solution at 25°C using ellipsometer and coulometric techniques. Films found on the alloys were progressively thinner as the alloy concentration was increased. The correlations with potential dependence suggest that the inverse logarithmic law may be applicable. The optical constants of the alloys in the film-free condition were similar but different from those of the films. The optical constants of the films on the alloys were similar.