This study was undertaken to assess a post-hybridization amplification system for increasing the sensitivity of in-situ hybridization with oligodeoxyribonucleotide (oligonucleotide) probes. The technique employs a multilayer streptavidin-biotinylated link protein amplification technique, similar to that used in the ABV histochemical amplification system, to attach increasing numbers of radiolabelled streptavidin molecules to a biotinylated ologonucleotide probe. In tissue sections the amplification technique increases the signal-to-noise ratio dramatically, increasing the sensitivity of in situ hybridization and reducing the autoradiographic exposure time. On an artificial medium the amplification technique has been shown to increase the hybridization signal 100-fold when compared with a directly radiolabelled oligonucleotide probe. The technique could be used to compare relative amounts of target molecule, there being a linear relationship between the detectable signal and the log of the concentration of the target molecule.