We engineered Lactobacillus paracasei to produce a dsRNA that would trigger RNAi-induced silencing of an essential gene in the nematode Caenorhabditis elegans. The dsRNA-expressing L paracasei can be used in experiments conducted on culture plates and may also be used as an orally administrable dsRNA carrier for humans and other mammals. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.