Freeze-dried cells of Thiobacillus thiooxidans exhibited sulfide-oxidizing activity similarly to intact cells, hut the activity level was reduced during storage. The decrease in the activity was more marked when the freeze-dried cells were stored at higher temperature than -20 degrees C and under more aerobic conditions than 0% of oxygen partial pressure (pO(2)). Nonreducing disaccharides such as trehalose and sucrose were effective in maintaining the sulfide-oxidizing activity of the freeze-dried cells. The freeze-dried cells prepared in the presence of 10% (w/v) nonreducing disaccharides showed more than 80% of the initial activity for 60 d even though the cells were stored at 25 degrees C under atmospheric conditions. The freeze-dried cells mere used as a bacterial deodorant for removal of hydrogen sulfide (H2S) from gas phase.