Most substances used for sterilizing surfaces at room temperatures do not kill bacterial spores. Beta-propiolactone (BPL) is a liquid which exerts a strong bactericidal action on the surfaces of objects immersed in aqueous solutions of it or exposed to its vapor phase. In the present experiments it was used in three ways, being vaporized by heat in air at atmospheric pressure, vaporized at room temperature under reduced pressure, and applied as an aerosol by means of nebulizers. Five test-organisms, including Clostridium sporogenes, were used, and a variety of instruments heavily contaminated with them were sterilized at room temperature. In addition, practical experience with a wide variety of apparatus has been accumulated over a period of 16 months. Beta-propiolactone has a broad field of application provided its limitations are recognized and it is handled, like other bactericidal agents, with due regard for its toxic properties.