The investigations were carried out in the borderland of the ?redni (Makowski) and Wyspowy Beskids (the Carpathians). In the River Bogdan?wka flowing out from the range of the Koskowe G?ry Mts (the Carpathians) Paramecium biaurelia was found. The results of the present work together with the previous data (KOMALA 1997, 1998) indicate that Paramecium biaurelia is more common in the investigated Carpathian region than other species of the aurelia complex. The results also indicate that this species is much more adaptive for acidic waters. Perhaps this ability makes the species capable of invading the marginal ecological niches more easily than is the case with other species of the group.