Abstract: Provided is a system for indicating exposure to a chemical vapor sterilization process. This system comprises a composition applied to a suitable support, which composition comprises a component which is chromatically transformed by the action of a vapor phase sterilant. In particular, the present invention is applicable to a system for indicating exposure to a hydrogen peroxide vapor sterilization process, with the component which is chemically transformed being so transformed in the presence of vaporous hydrogen peroxide. The composition comprises at least the component which is chemically transformed by the action of the hydrogen peroxide, but may also contain additional ingredients or components. For example, the composition also generally comprises a binder to aid in applying the composition to a suitable support or substrate.