chimaera• A quite different way of creating a chimaera is to fuse two early mouse embryos.• The embryo is thus a chimaera, a mosaic of two different kinds of cells.• Two out of 160 G418-resistant D3 clones were found to have the targeted mutation and clone 515 gave rise to germ-line chimaeras.• Germ-line chimaeras were obtained from both clones.