Abstract: A comprehensive overview is given concerning the in situ hybridizaiton tecnhiques using non-radioactively labelled probes. Details are given on the preparation of the probes with different reporter moelecules and on the corresponding revealing assays. The development of non-isotopic labeeling methods for nucleic acid probes has facilitated the diffusion of the in situ hybridizaiton techniques to the research as well as to the clinical pathology laboratory. Non-radioactive probes have serveral advantages over the radiolabelled ones, including cost, shelf-life, safety and, last but not least. resolutions of the signal.