Characteristics of G-proteins were studied in renal medulla of rats and mice of different ages. It was established that G-protein alpha-subunit gene expression has a specific dynamics with maximum on the 5-8-th day of life and at the end of weaning. It was shown that vasopressin does not stimulate G-protein GTPase activity in membrane preparations from immature kidneys. The differences of G-protein chromatographic characteristics were revealed. It is suggested that the development of vasopressin sensitivity of the kidney is related with the changes in G-protein system.