Fume aerosols of zinc oxide were generated by nebulization of aqueous solutions of zinc acetate (30 milligrams zinc acetate per milliliter water), with subsequent thermal vaporization and chemical degradation to the oxide. A Retec nebulizer operated with compressed air was used to generate the zinc acetate mists which were passed through a quartz tube furnace (1150°C) to dry the droplets and degrade the acetate to the oxide form. Ultrafine particles were formed in this process, demonstrating that zinc acetate was vaporized as aerosol entered the heated tube prior to thermolysis. The few larger particles probably represent those larger droplets which do not completely vaporize prior to thermolysis. Cascade impactor samples indicated a mass median aerodynamic diameter (MMADar) of 0.8±0.1 (SD) µm with geometric standard deviation (ag) of 2.9±0.5 (SD). About 25% of the zinc was associated with particles smaller than 0.3 µ in aerodynamic diameter, equivalent to spherical particles smaller than 0.09 µm in geometric diameter.