Intra-individual tissue-specific restriction fragment length polymorphism (RFLP) has been demonstrated in DNA isolated from different mammalian tissues using cDNAs of α- and β-subunits of Na+, K+-ATPase as hybridization probes. We propose that the RFLPs could result from gene rearrangements in the gene loci for the α- and β-subunits of Na+,K+-ATPase. The changes in restriction patterns have been shown to occur during embryonic development and tumor formation. In addition, the tissue specificity of the expression of different genes of the family of Na+,K+-ATPase genes and their low expression in tumor cells have been demonstrated. © 1987.