We have modified and shortened the routine fluorescence in situ hybridization (FISH) technique by using microwave or formalin pretreatment for artificially aging and microwave heating only for dehydrating the regular chromosome preparations. The all-human telomere probe (Oncor, Inc., Gaithersburg, MD) was used on murine K-1735 clone X-21 melanoma cells for this purpose. The intensity of signals obtained by our modified technique(s) was comparable to that obtained by the routine procedure. However, pretreatment of slides with hydrogen peroxide (H2O2) completely obliterates the FISH signals.