The objective of this study was to estimate the joint effects of CSN3 and LGB genotypes on breeding values of milk production parameters. CSN3 (kappa-casein) and LGB (beta-lactoglobulin) genotypes of 120 Czech Fleckvieh sires were detected using the PCR-RFLP method. Breeding values of sires were obtained from the Official Database of Progeny Testing. Ten genotype combinations were detected. Genotypes ABAB (25.0 %), ABAA (13.3 %) and ABBB (13.3 %) were the most frequent. Significant effects of genotype combinations on breeding values for fat and protein content were found. The highest breeding values for milk (+621 kg) and protein (+15.8 kg) yields were associated with genotype combination ABAA, while the highest breeding values for content parameters (+0.15 % for protein content and +0.55 % for fat content) were associated with genotype combination BBAB.