A direct inoculation method for sterility testing veterinary biologics was compared with a closed membrane filtration method (Steritest). The filtration method detected extraneous contamination in 29% more batches of biologics than the direct inoculation method. Live viral biologics produced in cell culture were found to be the only product type that could be filtered; hence the filtration method cannot be recommended universally as a replacement for the direct inoculation method.