Sterilizing filtration process variables can cause unpredictable results and post-filtration integrity test values that are not representative of those obtained during validation of the filtration process. This paper discusses several points to consider in sterilizing filtration designed to assure the validated process is robust and consistently yields a sterile filtrate. These points include pore- and particle-size distributions, the use and choice of prefilters, pore configuration, and the use of redundant (serial) filtration.