Prospections on helminth fauna of rodents were carried out in the Cedrino river (Eastern of Sardinia island). Twelve Rattus rattus (L., 1758) and eight Mus domesticus (Schwarz & Schwarz, 1943) were captured by Sherman traps. Parasitological study revealed in R. rattus the presence of an intestinal helminth belonging to the genus Maritrema (family Microphallidae). The transmission of this Digenetic Trematode among vertebrates involves the participation of aquatic invertebrate organisms, molluscs and crustacea, acting as intermediate hosts. Dissection of 117 individuals of the Amphipod Crustacea Gammarus italicus, collected in the same biotope, allowed the detection of encysted metacercariae. These larvae constitute the infesting stage of the parasite for vertebrates, acting these as definitive hosts ingesting parasitized crustacea as preys. Adults of Maritrema sp. were also obtained experimentally in the laboratory mice (Mus domesticus CD1 strain). These were infested by inoculating them, using gastric probe, metacercarial cysts isolated from G. italicus. Post-infection mice dissection was performed at different intervals of time getting adults in various maturity stages. Experimental facts confirm that Maritrema sp., as it occurs in other trematodes, do not present strict specificity to the definitive host, being able to develop as well in Mus. In nature, the presence or absence of this digenean in mammals species will be dependent of host ethological factors, mainly related to feeding habitats. This study was partially supported by the ?Comissionat per Recerca i Universitats de la Generalitat de Catalunya? 2001SGR00088.