Planar organic contaminants are known to induce specific biological activity (e.g. aryl hydrocarbon hydrolase and ethoxy resorufin-o-deethylase). An unequivocal identification and accurate measurement is essential in order to correlate the potential biological effect to these compounds. Pyrenyl-silica high-performance liquid chromatography allows an effective separation of these planar compounds from most biological co-extractants and from each other. This group of planar compounds includes specific chlorobiphenyls, polycyclic aromatic hydrocarbons, polychlorodibenzo-p-dioxins, polychlorodibenzofurans and polychlorinated naphthalenes.