The study was carried out in a Polish Black-and-White cattle population, represented by 167 AI sires, 200 young tested bulls, 190 bull-dams, and 606 randomly chosen cows from commercial herds. The fragment of the bovine prion protein gene (PRNP) coding the octapeptide-repeat sequence, was identified by PCR analysis. Two different gene variants of 349 bp and 373 bp in size, produced three genotypes: PRNP 6/6, PRNP 6/5 and PRNP 5/5, respectively. Allele frequency in all examined populations, on average 0.894 for PRNP 6 and 0.106 for PRNP 5, shows a significant difference between the group of cows from commercial herds, characterised by high frequency of PRNP 5 (q = 0.137) in comparison to AI sires (q = 0.077), young tested bulls (q = 0.052) and bull-dams (q = 0.084). Moreover, both analysed female groups of bull-dams and cows from commercial herds are distinguished by the presence of PRNP 5/5 homozygous animals, which were not recorded in the AI sires and young tested bulls, and had never been recognised in earlier examined Holstein-Friesian populations. Analysis of the genetic equilibrium indicates a very high conformity between observed and expected number of animals in the separate PRNP genotype groups. However, some tendency of difference is observed in highly selected cows, qualified as bull-dams on the basis of very high level of milk performance traits.