Multicolor fluorescence in situ hybridization (mFISH) assays are now indispensable for precisely describing complex chromosomal rearrangements and marker chromosomes. The routine application of such techniques to human chromosomes began in 1996 with the simultaneous use of all 24 human whole-chromosome painting (wcp) probes in multiplex FISH (M-FISH) and spectral karyotyping (SKY). This chapter reviews the available mFISH approaches that use wcp probes, and describes basic protocols for M-FISH and SKY.
