The karyotype of swamp minnow,Eupallasella percnurus(=Phoxinus percnurus) from northern part of Poland was studied by conventional Giemsa staining and Ag-NOR technique. The diploid chromosome number 2n= 50, was composed of 5 pairs of metacentric, 15 pairs of submetacentric and 5 pairs of subtelo- to acrocentric chromosomes (NF = 90). Two pairs of NORs bearing chromosome were detected. They were located terminally on the short arms of one pair of medium sized submetacentric and on one pair of medium sized subtelocentric chromosomes. Most of the related species from the genusPhoxinusandMorocohad diploid chromosome number 2n= 50 and their karyotypes were also characterized by the biggest acrocentric pair. Most of the North American minnows species had one pair of NORs bearing chromosomes.