The use of the Kovats retention indices for standardization in gas chromatography enables the compilation of gaschromatographic data and the exchange of those data between different laboratories. Factors important for reliable determination of the retention indices, in particular the temperature dependence, are discussed. The gain in information due to the application of the retention indices and their differences on two stationary phases is demonstrated by means of tables with indication of their efficiency in searching for unknown compounds from such files. In the supplement retention indices on OV-1, OV-17 and their differences for 72 compounds frequently encountered in toxicological analyses are given.