The human genes for thymidine kinase,galactokinase and procollagen type I,located on chromosome 17,have been transferred to cultured mouse cells. In unstable cell lines the transferred genetic material is shown to exist independently,whereas in stable cell lines the transferred material has become associated with chromosomes of the recipient cell. The size of the transferred genetic material exceeds 1% of the human haploid genome in some of the transformed cell lines. In addition,the data indicate a gene order of: centromere-galactokinase-(thymidine kinase,procollagen type I),on the long arm of human chromosome 17. © 1979 Nature Publishing Group.