We evaluated the ability of an electrostatic air cleaner and negative ionizer (Bionaire 1000, Biotech Electronics, Ltd) to cleanse indoor air of mold spores. Significant reductions in the number of mold colonies were observed when the air cleaner was operated alone. We found no significant decrease in the circulating amounts of mold spores over baseline with the additional use of the negative ionizer. Though there were day-to-day variations in the numbers of spores, these changes remained significant.