Abstract: A disposable biological test pack for determining the efficacy of ETO gas sterilizers comprising a plastic housing which in turn houses a plastic vial holding biological spores. The plastic housing is closed at one end by a rubber cap and at the other end by an end plug with a porous paper/plastic insert or plug which allows sterilant to enter the tube in metered amounts to kill the biological spores contained within a plastic vial otherwise referred to as a self-contained biological indicator. If insufficient sterilant is present the biological spores will survive upon incubation which indicates a failure of the sterilization equipment. The present invention is unique in that it uses low porosity filter material to restrain the entry of the sterilant. By doing so the test pack stimulates the performance of the AAMI standard test pack.