By means of nucleotide sequencing in a library of clones, containing cDNA of Bos taurus mammary gland, a clone corresponding to kappa-casein has been identified. In addition, the region encoding for the complete nucleotide sequence of cDNA of kappa-casein B macropeptide has been detected. The nucleotide changes in the DNA sequence have been identified which mean that the isolated clone corresponds to the genetic variant B of kappa-casein.