A method for disinfecting a volume or surfaces bounding a volume comprising nebulizing a solution comprising a sterilizing agent in a solvent having a lower boiling point than the sterilizing agent to form a nebulant. The nebulant is subjected to energy of a kind and for a duration sufficient to vaporize solvent in preference to sterilizing agent to increase the concentration of the agent in the nebulant particles. Vaporized solvent is removed from the gas stream at or above atmospheric pressure and, if necessary, the nebulant is cooled to below 70° C. The volume or surfaces are exposed to the nebulant for a time sufficient to sterilize said volume or surfaces. Also, apparatus for carrying out the method.