A method for producing cell lines or individual organs, differentiable donor cells being supplied to a morula or blastocyst which is cultivated under conditions that ensure a further development of the morula or blastocyst in stages in which newly formed cell lines having a higher degree of differentiation occur, as well as isolation of the cell lines or further differentiation of the cell lines into organs. The method according to the present invention is distinguished in that the cells of the morula or the internal cell mass of the blastocyst have a restricted survivability in comparison to the particular wild type or their survivability is reduced through suitable cultivation conditions, and the donor cells supplied to the morula or blastocyst have varying degrees of differentiation. A significantly shortened cultivation period of the donor cells may thus be achieved in comparison to typical methods, through which the provision of natural stem cells is favored, and perhaps made possible for the first time. The blastocysts may also be used by being transferred into a surrogate mother animal.