Fluorescence in situ hybridization (FISH) is the gold standard methodology for gene copy number determination in cultured cells, metaphase spreads, tissue samples or cytologic specimens. While it has primarily been used as a research tool during the last decade, there is a growing demand for the use of FISH as a diagnostic tool. In such a setting, analysis speed, reliability and cost efficiency become important parameters. Perhaps the most critical step in the FISH procedure is the proper adjustment and maintenance of temperatures for DNA denaturation and probe hybridization. We have compared different devices for slide heating to estimate their suitability for FISH analysis. Our study demonstrates that programmable slide incubators are profoundly superior to the classical waterbath for FISH analysis. The Eppendorf add-on hybridization station is an attractive alternative for owners of the Thermomixer comfort device that allows for high-quality FISH analysis at low cost for machinery.