The rapid determination of pentachlorophenol and tetrachlorophenols in animal materials by high-performance liquid chromatography (HPLC) on porous silica is described. Non-fatty substrates are digested in alkali and the chlorophenols extracted as ion pairs. Fatty materials are extracted with ethyl acetate-hexane after acidification. Extracts are cleaned up on "Sep-Pak" silica or Florisil cartridges. Penta- and tetrachloroanisoles are recovered by the extraction procedures and can be determined by gas chromatography if required. Mean recoveries of the chlorophenols were 73-108% at fortification levels of 0.1-10 mg/kg. A concentration of 0.1 mg/kg can readily be determined and the method can be adapted to reach about 1 microgram/kg. Identities can be confirmed by ion-pair HPLC on a reversed-phase column.