Cell hybrids between hypoxanthine guanine phosphoribosyl transferase (HGPRT)-deficient mouse cell lines (A9 or RAG) and each of 12 different human fibroblasts (GM cells) containing various X/autosome translocations were formed, selected and isolated. Several human chromosomes including an X/autosome translocation carrying HGPRT locus were found in these hybrid cells. To construct A9 cell clones that contain a single X/autosome translocation, micro-cell fusion was undertaken to transfer these chromosomes from the hybrids to A9 cells. Karyotype analysis revealed that most of the resulting micro-cell hybrids contain, in a background of mouse chromosomes, only the human X/autosome translocations which were present in the GM cells used for cell hybridization. Sublines of A9 cells were established containing the following autosomal segments: 1q23----1qter; 1q12----1pter; 3p12----3pter; 3q21----3qter; 11q13----11qter; 11q13----11pter; 11p11----11qter; 11q23----11pter; 12q24----12pter; 16q24----16pter; 17q11----17pter.