We established chromosomal homologies between all chromosomes of the human karyotype and that of an old world monkey (Macaca fuscata) by chromosomal in situ suppression (CISS) hybridization with human chromosome specific DNA libraries. Except for the human chromosome 2 library and limited cross-hybridization of X and Y chromosome libraries all human DNA libraries hybridized to single GTG-banded macaque chromosomes. Only three macaque chromosomes (2, 7, 13) were each hybridized by two separate human libraries (7 and 21, 14 and 15, 20 and 22 respectively). Thus, an unequivocally high degree of synteny between human and macaque chromosomes has been maintained for more than 20 million years. As previously suggested, both Papionini (macaques, ba...