The results of preliminary karyological investigations of two geographically distant and morphologically slightly different Polycelis felina (Daly.) populations from central Croatia are reported. The results have shown that individuals of both populations are diploids, with the same chromosome number in their neoblasts (2n=18). Their karyotypes were composed of nine chromosome pairs, three of them are metacentric and the other six are submetacentric. Statistical evaluation of data indicated that both populations of Polycelis felina (Daly.), despite minor differences observed between them, belong to the same karyological biotype.