NK cells play an important role in blastocyst implantation and pregnancy preservation. It was found that the minimum non-toxic dose of recombinant G-CSF for K-562 and NK-92 cell line - 400 000 ME. In the same concentration, the drug G-CSF reduces the cytotoxic activity of NK-92 cells against K-562 cell line and trophoblast cells of the Jeg-3 line. The obtained results suggest the presence of a similar effect of the drug G-CSF in vivo.