We have numerically examined the effects of adopting the absorption efficiencies predicted by the Mie theory for spheres on the maximum temperature of pure olivine and pure iron micrometeorites entering the earth's atmosphere and pure water ice micrometeorites entering the Uranian atmosphere. We found that particles of micron and submicron size with the optical properties that characterize these substances tend not to radiate away their frictional heat of entry as efficiently as classical micrometeorite theory predicts. Consequently, the degree to which these particles are heated and altered during entry is increased. We conclude that micron and submicron-sized particles are more realistically treated as Mie spheres than as blackbodies, when accurate values exist for the imaginary index of refraction at wavelengths of a few microns. ¿ American Geophysical Union 1991