Abstract: A protective housing for a biological indicator for testing the effectiveness of a sterilization procedure comprises a tube constructed of a liquid impermeable and gas-nonabsorptive polymer, a cap assembly having an aperture that allows sterilant to enter the housing during the sterilization procedure and contact the biological indicator, and an absorptive material in the cap assembly to prevent condensed sterilant from entering the housing and contacting the biological indicator. During a sterilization procedure the protective housing reduces premature inactivation of biological indicators, especially biological indicators that measure the effectiveness of a sterilization procedure by monitoring an enzyme whose activity can be correlated with the viability of at least one microorganism commonly used to monitor sterilization efficacy.