The chromosome morphology of four populations ofDugesia gonoce-phalas.l. from various European localities is described. Three populations (S1, V26 and V35) showed diploid complements of 16 metacentric chromosomes, whereas one population (V28) has a triploid complement of 24 meta- and submetacentric chromosomes. The karyotypes of the populations show small variation of chromosome length and centromere position, which do not enable the identification of individual chromosomes. For a statistical approach of this problem, the 95% confidence limits of relative length and centromeric index were calculated for each chromosome and set out in two dimensional scatter diagram. It is argued that in cases where chromosomes decrease gradually in relative length and show similar centromeric indices, matching of chromosomes in pairs is statistically unsound. Chromosome differentiation techniques were introduced to obtain characteristic banding patterns for chromosome recognition. Tentative results obtained with the BSG-technique showed clear C-bands at the telomeres and centromere regions of some chromosomes. Silver (Ag-As) staining demonstrated the presence of Ag-NORs in two chromosomes of one of the populations. Quinacrine staining of squashed blastemas revealed rather uniform fluorescence intensity at all chromosomes.