mRNA coding for beta-subunit of Na+, K+-ATPase from pig kidney is about 24-25S as deduced from the hybridization pattern of poly (A)+-RNA with two synthetic oligonucleotides structurally corresponding to two peptides isolated from the tryptic hydrolyzate of beta-subunit. Cloning of cDNA allowed to determine the complete structure of the gene and to deduce the amino acid sequence of beta-subunit of Na+, K+-ATPase. The beta-subunit contains 302 amino acid residues and the protein is not processed at the N-nor at the C-terminus.