The expression of genes coding for alpha and alpha III isoforms of Na+,K+-ATPase alpha-subunit has been studied in human kidney, brain, thyroid and liver cells. The expression was shown to be subjected to a tissue-specific control and also depended on the developmental stage. The tissue-specific expression of genes coding for different isoforms of the catalytic subunit of Na+,K+-ATPase perhaps may be attributed to various functions of proteins belonging to this family.