Abstract: A self-contained biological indicator for evaluating the efficacy of sterilization processes utilizing hydrogen peroxide and hydrogen peroxide/peracetic acid plasma and vapor as the sterilant is disclosed. The self-contained biological indicator includes a translucent, vapor-permeable, container including a source of dormant microorganisms, a sealed ampule containing a culture medium that is capable of promoting the growth of surviving microorganisms, a neutralizing tablet that is capable of decomposing hydrogen peroxide sterilant, and an actuating mechanism that permits mixture of the source of microorganisms, culture medium and the hydrogen peroxide neutralizing tablet to be brought into contact from the exterior of the indicator. In one embodiment the self-contained biological indicator is comprised of a plurality of generally cylindrical, telescoping vials being operable from an unsealed, sterilization test configuration to a sealed and activated configuration for incubation.