Messenger RNA, coding for the alpha-subunit of the Na+, K+-ATPase, was isolated from outer medulla of pig kidney. Within 25S-26S region the mRNA yields a band of specific hybridization with three oligonucleotide probes synthesized according to data on structures of three peptides isolated from the tryptic hydrolysate of the protein. Translation of the enriched poly(A+)-fraction of RNA in Xenopus laevis oocytes followed by the immunochemical identification of the products confirmed the presence of RNA coding for the desired protein. This RNA preparation was used for synthesis and cloning of double stranded cDNA.