Titanium dioxide (TiO(2)) is known to confer photocatalytic bactericidal effects under ultraviolet (UV) irradiation. Few reports are available, however, on the clinical applications of TiO(2) particle mixtures. Our objective in the present research was to evaluate the in vitro bactericidal effects of a TiO(2) particle mixture in a nutrition-rich biological environment. A bacterial suspension of Staphylococcus aureus and epidermidis 3 x 10(3) CFU/mL was added to a TiO(2) particle mixture (0.038 mg/mL) containing mainly sodium percarbonate and citric acid. To simulate a biological environment, 40 microL of 10% bovine serum albumin was added and the culture temperature was maintained at 37 degrees C. The resulting product was irradiated by UV light and the bacterial survival rate was calculated for each time of UV irradiation. In the control sample treated with distilled water + UV, the bacteria survived at a high rate even after 180 min. In the TiO(2) mixture + UV sample, meanwhile, the bacterial survival rate dropped to 43.8% and 6.0% of the baseline values in S. aureus and S. epidermidis, respectively, after 60 min of UV irradiation. The photocatalytic antibacterial action of the TiO(2) particle mixture was high even in a protein-rich biological environment.