The potential of protostrongylid first-stage larvae (L 1 ) to survive passage through the alimentary canal of non-infected mammals was investigated. Parelaphostrongylus tenuis L 1 were collected from feces of an experimentally infected white-tailed deer ( Odocoileus virginianus ). We utilized two red deer ( Cervus elaphus ) and four laboratory rats ( Rattus norvegicus ) which were each fed the L 1 of P. tenuis . Larvae were recovered, intact and alive, from the fecal samples of all six animals. Larvae of P. tenuis , and probably of other related species, can survive passage through the alimentary canal of uninfected mammals and they can be collected from feces using the Baermann technique and other related larval extraction methods. Rain water was found to be successful in the dispersal of P. tenuis L 1 from the feces of infected animals. These findings raise the possibility of ingestion of L 1 and their subsequent passage, by uninfected animals. This potential for false-positive diagnosis of infection in live animals necessitates accurate interpretation of a host's infection-status. Such findings reinforce the need for a reliable method of diagnosing infections in live animals.