Dual color FISH with whole chromosome and pan-centromere probes facilitates rapid detection of stable structural aberrations such as translocations. This approach should allow analysis of translocations for assessment of genetic damage at long times after exposure or as a result of chronic exposure during a long period of time. Multi-color FISH with locus specific probes allows assessment of the frequency of cells carrying specific aberrations known to be associated with tumorigenesis, analysis of the series of genetic changes that occur during tumor evolution and correlation between genotype and phenotype. The power of FISH for analysis of random and tumor related events will increase steadily as informative probes are developed during the course of the International Human Genome Project.