Based on the chromosome orientation-FISH (CO-FISH) method, replicative detargeting FISH (ReD-FISH) was developed as a unique tool for investigating the replication patterns of telomeres on individual chromosome arms. This method is also suitable for studying telomeres of species from different animal classes for which well-proliferating cell cultures can be established and maintained. ReD-FISH is based on the pulsed incorporation of labeled brominated nucleotides into replicating DNA, the destruction of regions containing brominated analogues, and standard FISH with single-strand-specific probe(s).