The present invention concerns compositions and methods for the introduction of specific genetic changes in endogenous genes of the cells of an animal. The genetic changes are effected by oligonucleotides or oligonucleotide derivatives and analogs, which are generally less than about 100 nucleotides in length. The invention provides for macromolecular carriers, optionally incorporating ligands for clathrin coated pit receptors. In one embodiment the ligand is a lactose or galactose and the genetic changes are made in hepatocytes. By means of the invention up to 40% of the copies of a target gene have been changed in vitro. Repair of mutant genes having a Crigler-Najjar like phenotype and Hemophilia B phenotype were observed.