Development of the gene engineering techniques has raised worries that they will be used for construction of organism endangering humansand environment. In 1975 at the Asilomar conference, geneticists from many countries decided that genetic engineering brings more benefitsthan threats. In last years a new CRISPR-Cas technique emerged . It allows to make the precise changes in genomes, e.g. to inactivate particulargenes or to replace mutated genes by their wild-type alleles. Inactivation in mice of genes corresponding to those whose mutations causethe genetic diseases in man allows to get model organisms for studying the etiology of given disease and for working out the methods of itscuring. This technique can be applied for repairing genes whose mutations result in metabolic diseases and cancer. Some voices were raisedthat the technique can be potentially used for the “improvement” of man, what would create many ethical and social problems. Geneticists,ethicists and lawyers gathered in 2015 at the Washington conference, discussed these problems and proposed rules for their solving.