Adult Sigmodon hispidus, were given 50 third-stage larvae of Angiostrongylus costaricensis orally, intraperitoneally, subcutaneously, and on abraded and unabraded skin. Larvae could not penetrate unbroken skin but established normal infections in the cecal vasculature by all other routes. Significantly more adults were recovered after oral and intraperitoneal inoculation than subcutaneously or through abraded skin. In a single animal given larvae subcutaneously, adult worms were recovered from the pulmonary arteries, an abnormal location for this species of metastrongylid nematode, which usually occurs in the ileocolic mesenteric arteries.