When the energy of animal cells is the ability to regulate their own volume. Even under hypotonic stress the cells can readjust their volume after transient osmotic swelling by a mechanism known as regulatory volume decrease (RVD). The nature of the regulatory mechanisms governing the volume changes in embryonic cell during RVD is not clear. Osmotic adaptation in a blastomere of two-cell mouse embryo has been studied employing the direct measurement of cell volume with laser scanning microscopy followed by three-dimensional reconstruction. The hypotonicity was created by replacing 140mM NaCl in Dulbecco`s solution with 70mM NaCl. The keeping of the intact volume of the embryo compartments was based on freeze-drying technique. A Z-stack of optical slices was obtained in a confocal microscope (Zeiss, Germany). 3-DR was performed in the 3ds max medium. Our data indicate that hypoosmotic incubation for 10 minutes resulted in the swelling peak of blastomere volume ((94±8) x 10<sup>3</sup>mm<sup>3</sup>, these and all results below are presented as the mean and the standard deviation). After 60 minute incubation the cell volume was recovered to control level ((57±4) x 10<sup>3</sup>mm<sup>3</sup>). Exposure of embryonic cells to the hypotonic K<sup>+</sup>-free medium did not influence on the kinetics of cell osmotic behavior. After 60 minute incubation in hypotonic Dulbecco`s with Cytochalasin B blastomere's volume was calculated as (86±6) x 10³mm³. Na⁺/K⁺-ATPase inhibition does not influence on RVD of the embryonic cells, but volume recovery specific for hypotonic shock is blocked by the alteration of F-actin organization.