Pentachlorophenol (PCP) is extracted from soil and fish with 0.1M potassium hydroxide. After adjusting the pH to below 7, the PCP is extracted with toluene, methylated with diazomethane, and analyzed by electron-capture gas chromatography. As little as 0.5 p.p.b. of PCP can be detected in soil or fish. In 1 liter of water it is possible to determine 0.01 p.p.b. Recovery of added PCP is in the range of 80 to 100%. A method for the preparation of PCP trimethylsilyl ether is described, and this derivative is used for qualitative test. A further identification of PCP is made with a mass spectrometer.