The aim of this work was to determine allele and genotype frequencies at the casein loci, alphaS1-casein (CSN1S1), beta-casein (CSN2) and kappa-casein (CSN3) in two endangered Czech sheep breeds. The study was carried out on 265 sheep (133 Sumava, 132 Walachian) by means of PCR-RFLP and Light Cycler Analysis. These breeds are kept mainly for their good combined efficiency (milk, meat, wool). In particular, the genetic variant C at the CSN1S1 locus occurred with high frequency in both breeds Sumava (0.981) and Walachian (0.992). Variants A and D were either “absent” in Walachian (A=0.008, D=0), or present with a very low frequency in Sumava (A=0.008, D=0.011). Molecular analysis of the CSN2 locus showed that the genetic variant A were predominant, had higher frequency (Sumava, 0.778; Walachian, 0.829) than did variant G (Sumava, 0.222; Walachian, 0.171) in both sheep populations. The CSN3 locus was found to be monomorphic, with no polymorphism typed in either population. According to Hardy-Weinberg equilibrium, both breeds were in genetic equilibrium at the loci CSN1S1 and CSN2 (P