A method of sterilizing articles using hydrogen peroxide as sterilant, comprising the steps of: a. evacuating a closed chamber containing an article to a pressure P 1 below atmospheric pressure; b. injecting a predetermined amount of sterilant vapor into said closed chamber in a pre-pulse sufficient to establish a desired initial level of sterilant into said chamber and raise a pressure in the closed chamber from the pressure P 1 to a pre-pulse pressure P p ; c. following the pre-pulse injecting of the predetermined amount of sterilant vapor to raise the pressure to the pre-pulse pressure P p , evacuating said closed chamber from the pre-pulse pressure P p to the pressure P 1 ; d. introducing only sterilant vapor into the closed chamber in an amount effective to raise the pressure in the closed chamber to a predetermined second subatmospheric pressure P 2 ; e. allowing the introduced amount of sterilant vapor to diffuse throughout the closed chamber and into the article for a predetermined period of time which is less than or equal to twice the half-life of the sterilant vapor in the closed chamber; f. introducing a compression gas into the closed chamber in an amount effective to raise the pressure in the closed chamber to a third subatmospheric pressure P 3 in a compression time period, wherein the third pressure is greater than the second pressure and wherein the pressure differential between the third pressure and the second pressure is effective to drive the diffused sterilant vapor further into the article than the vapor has diffused such that the sterilant vapor substantially penetrates the article; and g. repeating steps (c) through (f) until sterilization of the article is achieved. a. evacuating a closed chamber containing an article to a pressure P 1 below atmospheric pressure; b. injecting a predetermined amount of sterilant vapor into said closed chamber in a pre-pulse sufficient to establish a desired initial level of sterilant into said chamber and raise a pressure in the closed chamber from the pressure P 1 to a pre-pulse pressure P p ; c. following the pre-pulse injecting of the predetermined amount of sterilant vapor to raise the pressure to the pre-pulse pressure P p , evacuating said closed chamber from the pre-pulse pressure P p to the pressure P 1 ; d. introducing only sterilant vapor into the closed chamber in an amount effective to raise the pressure in the closed chamber to a predetermined second subatmospheric pressure P 2 ; e. allowing the introduced amount of sterilant vapor to diffuse throughout the closed chamber and into the article for a predetermined period of time which is less than or equal to twice the half-life of the sterilant vapor in the closed chamber; f. introducing a compression gas into the closed chamber in an amount effective to raise the pressure in the closed chamber to a third subatmospheric pressure P 3 in a compression time period, wherein the third pressure is greater than the second pressure and wherein the pressure differential between the third pressure and the second pressure is effective to drive the diffused sterilant vapor further into the article than the vapor has diffused such that the sterilant vapor substantially penetrates the article; and g. repeating steps (c) through (f) until sterilization of the article is achieved. <EOS>