Acetone is a potent bactericidal agent and has considerable value for the routine disinfection of surfaces. The reason for the poor showing of acetone in previously reported tests was that it was not used in concentrated form, and our tests also confirmed its relative ineffectiveness when diluted. The inability of acetone to eliminate spores is an important disadvantage but most commonly used bactericidal agents also are deficient in this respect. Although acetone is active in the presence of protein it does not penetrate blood clots. Therefore, instruments should be cleaned of blood and tissue fragments before using acetone to disinfect them, as with other methods of sterilization. Acetone can make ordinary sterilizers unnecessary in our offices. I believe that it is a superior antiseptic for use in sterilizing sharp instruments in the operating room and can be used for all instruments when autoclaving or gas sterilization is not feasible or not available.