Rat tracheal organ culture (TOC) supported replication of parainfluenza 1 (6/94) virus. Cell-associated and cell-free viruses were found after primary infection of TOC. In contrast to other mammalian systems, rat TOC was capable of maintaining 6/94 virus infectivity after primary infection. Rat TOC may be considered a potential indicator system that could be used to detect virus latent in human tissue.