We have studied the sublimation and breakup of single 100--200 μm frost particles levitated electrically at temperatures in the range -2 ¿C to -30 ¿C. Breakup rates were largely independent of temperature and humidity in this range but strongly dependent on particle shape. Irregular particles of high aspect ratio were most likely to break up. Sublimation (evaporation) was accompanied by an increasing aspect ratio. A linearized sublimation model, presented in the appendix, accounts for the observation that thin neck regions were not subject to enhanced sublimation rates. Estimates of the forces involved in breakup suggest that the breaking strength of these frost particles is considerably less than that of bulk ice. We discuss possible implications of our results for ice particle multiplication in clouds. ¿ 1998 American Geophysical Union