Whole chromosome painting libraries (WCPLs) have provided a very powerful tool to cytogeneticists. The technique allows the painting of specific chromosomes in metaphase spreads and in interphase nuclei (1 -4 ). The usefulness of WCPLs is particularly evident in identifying the chromosomal origin ofde novounbalanced translocations and marker chromosomes, or, more generally, in characterizing those cytogenetic cases in which the conventional approach based on banding techniques failed to elucidate the chromosomal rearrangement under study (5 ,6 ). Such cases are frequently experienced in cancer cytogenetics (7 ,8 ). WCPLs are usually derived from flow-sorted chromosomes.
