When analysing the karyotype of young Holstein-Friesian bull, two cell lines were observed - with chromosomes 60,XY and 61,XYY, in a culture of blood lymphocytes. The mean per cent of cells with karyotype 60,XY amounted to 72, while with karyotype 61,XYY - 28. The subsequent cytogenetical tests, conducted when the bull reached 16 months of age, also demonstrated the occurrence of two cell lines in cultures of skin, kidney, spleen and lung fibroblasts. The ratio of cells with karyotype 60,XY:61,XYY was as follows: 72:28 in skin, 68:32 in kidney, 62:32 in spleen and 61:39 in lung. Moreover, the examinations of meiotic chromosomes demonstrated the presence of bivalents XY and trivalents XYY. The bull showed a normal growth rate and live body weight and normally developed sexual organs. The evaluation of the bull’s semen, conducted at the age of 14 months, showed that it meets the standards accepted for sires maintained in AI stations. An analysis of the polymorphism of 11 microsatellite DNA sequences was performed for the bull examined and his parents, using a commercial StockMarks for Cattle Bovine II v. 2 PCR Typing Kit. An additional third allele was identified at locus ETH3, what indicates the presence of cell chimerism in the 60,XY/61,XYY bull examined.