Initially, the species of trematode Pleurogenoides medians Olsson 1876 was discovered and identified in ex. R.D.G., R.F. Germany, ex. U.R.S.S. (Hotenovskii, 1970), Romania (Radulescu et al. 1956b, Capuse et al.. 1957) Poland and other regions. In Moldova, this species was discovered for the first time in the intestine and stomach of amphibians from green ranids complex: Rana ridibunda, R. lessonae and R. esculenta in central zones of Codri forest. Some authors have described that hosts for this species of trematode may also include other amphibian species: Rana terrestris, R. temporaria, R. chensinensis, Tritirus vulgaris, T.cristatus, Pelobates toad, Bufo viridis, B. bufo, B. calama, Bombina bombina, Hyla arborea (Rijicov et al., 1980). Pleurogenoides medians Olsson in 1876 species description, the paper was based on the study of 419 specimens that were obtained from species Rana ridibunda, R. lessonae and R.esculenta caught from four natural basins and eight anthropogenic basins (Fig. 1). The body appearance can be round, oval or spindle-shaped, with a length from 0,507 to 1,149 mm and a width from 0,243 to 0,588 mm. Cuticle, except the tail is covered with small thorns. Oral sucker has a diameter of 0,066-0,118 x 0,053-0,132 mm, located less subterminal terminal. Ventral sucker has a diameter from 0,050-0,115 x 0,056-0,108 mm, located pre-equatorial. Intestinal branches are short and quite broad, reaching more or less the ventral sucker. Excretory orifice has a short channel with long branches, that reach the ventral sucker. Testicles 0,083-0,085 x 0,083-0,086 mm in diameter, have a round, irregular or oval shape, located on ,ventral side of the sucker. Copulatory organ is disposed in the first half of the body and reaches the ventral sucker. Genital orifice is located marginal to the glottis, the mid esophagus were at branching intestinal. Ovary may be a round shape, oval or irregular 0,045-0,147 x0,0420,134 mm in diameter, above the intestinal branches at some distance above the testicle or nearly touches. Seminal receptacle is round or elongated, positioned right of the ovarian or testicle and ventral sucker. Vitelogene glands are formed from small ammount of follicles situated to the rear of the oral cavity, at the level of the glottis or intestinal branch. Vitelogene glands are usually composed of two groups of follicles, separated dorsally, which can sometimes be omitted. Uterine loops are positioned postacetabulare and can not pass this level. Eggs diameter vary between 0,013-0,023 x 0,008-0,012 mm, at one of the poles has a cap, and on the other - a lower edge (Tab. 1). Biological cycle. For Pleurogenoides medians definitive hosts are anurans, in which is frequently detected this trematode. The first intermediate hosts are molluscs B. tentacle, L. limosa, P. corneus. Their infestation occurs after ingestion of eggs containing miracidia, which develops sporocysts. Have all the appearance and are located predominantly in the visceral connective tissue of the higher visceral sac and in cavity of gonad, less often in the region of the heart, kidney and the gut at the rear part of the molluscs. Depending on the size of sporocysts they contain from 1-2 up to 4-5 cercariae. The second intermediate hosts are various larvae of aquatic insects (dragonflies, beetles, ephemia, plecoptera, caddisflies) and crustaceans (Gammarus, Asellus). Metacercariaes of this species are observed at progenesis (larval multiplication). Occasionally, the trematode Pleurogenoides medians was found in lizards and river pike (Rijicova et al., 1980). Aknowledgement: The work was performed within the project 15.817.02.12F financed by Academy of Sciences of Moldova.