Protocol for In situ hybridization to human metaphase chromosomes using DIG-, biotin-, or fluorochrome-labeled DNA probes and detection with fluorochrome conjugates. Includes: Pretreatment of metaphase spreads on slides; Denaturation and hybridization; Single color fluorescent detection with immunological amplification; Multicolor fluorescence in situ hybridization (Multicolor FISH); Results obtained with human metaphase chromosome spreads.