Atom-probe analysis shows the depletion of chromium from the surface of stainless steel 410 tips subjected to heating in vacuum. Times necessary for depletion are lower by a factor of 104 than those found by Park et al. in which planar surfaces were analyzed by the x-ray appearance potential technique. This is explained on the basis of the great sensitivity of depletion rate upon the surface-to-volume ratio. The atom-probe specimens have a surface-to-volume ratio similar to catalytic powders, and thus the results of preferential evaporation, may be more realistic for the study of powder catalysts which are subject to annealing. The present work also cautions atom-probe experimenters in drawing conclusions from the abundance of atomic species after an alloy tip has been annealed in vacuum.