The karyotypes of four Acipenseriformes species, Acipenser gueldenstaedti, 2n = 250+_ 8, A. ruthenus, A. stellatus and Huso huso, 2n = 118+_2, are described. In all four karyotypes the majority of chromosomes are meta-and submetacentric macrochromosomes, and microchromosomes of different morphology make up about one third of the set. In A. ruthenus the NORs are located in the telomeric region of a pair of microchromosomes and at least in one pair of middle-size acrocentrics, and in A. stellatus and Huso huso also in the telomeric regions of at least one pair of microchromosomes. The modal number of active nucleoli in A. gueldenstaedti nuclei amounts to 6-8 (range 2-12), in A. ruthenus, A. stellatus and H. huso nuclei to 2-3 (range 1-6). The data obtained point to the tetraploid origin of Acipenseriformes species with 120 chromosomes and to the octoploid origin of species with 240-260 chromosomes.

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