Systematic genetic monitoring in populations allows to control the level of genetic diversity, to use the capabilities of marker selection, including the assessment of intra-breed differentiation, the formation of an optimal genealogical structure and selection for heterosis. The article provides information about the genetic structure of the populations of Belarusian Black-and-White cows at the lactoprotein loci CSN3, LALBA, BLG. In two farms at the LALBA, BLG loci, the most frequently encountered (from 42% to 51%) is the heterozygous genotype AB. At the CSN3 locus AA homozygotes were predominant (65% – 72%). Alleles had an almost equal frequency – 61% and 62% for LALBAA and 39% – 38% for LALBAB. The frequencies CSN3A and CSN3B had almost the same values – 0.806 – 0.853 and 0.194 – 0.147, respectively. In genetically equilibrium (χ2 <3.84) cow populations, the occurrence of the BLGA allele was 0.549 and 0.486, BLGB – 0.451 and 0.514. The average heterozygosity is determined at the level of 39.6% – 3.4%.