Continuous microindentation tests on electropolished, single crystal Fe(3wt%Si) and Ni surfaces with thin passivation layers exhibit sharp discontinuities in the load-displacement behavior. At the discontinuity, which occurs at a load of 1.8 mN for Fe(3wt%Si) and 0.1 mN for Ni, stresses below the indenter were close to the theoretical strength of the corresponding metal. Microindentation tests performed to loads less than the discontinuity point showed an elastic load-unload behavior. On removing the passive film with a NaCl or HC1 solution, strengths are one to two orders of magnitude smaller in the presence of the chloride ions. On evaporation of the liquid, the load at the discontinuity returned to its initial value due to repassivation, indicative of a passivation oxide layer with varying thickness. This conclusion was verified by ellipsometry. Even though the elastic load-unload behavior on the passivated surface suggests elastic behavior, both elastic finite element and non-linear, elastic perfectly plastic finite element solutions strongly suggest that this might not be the case. Several suggestions as to the reasons for the deviation from continuum theory are presented.