Photocurrent imaging of passive iron, both of pure metal and of an impure material in which grain boundary segregation was suspected, showed great heterogeneity with NaOH electrolyte, much less heterogeneity with Na 2SO 4 electrolyte. Effects of light intensity and electrode potential were spatially variable: the heterogeneity was such as to counsel caution in the interpretation of results based upon measurements averaged over the entire surface. It is speculated that the passive layer formed in Na 2SO 4 has a duplex morphology, with a uniform overlayer dominating the photoresponse, whereas in NaOH the film comprises a single barrier layer nucleated directly onto the metal.