1,2,3,4 and 1,2,4,5-tetrachlorobenzene are intermediates in the synthesis of various chlorinated compounds. Since personnel are being exposed to tetrachlorobenzene in the plant, studies on absorption, distribution and metabolism need to be conducted. Samples of 1,2,3,4 and 1,2,4,5-tetrachlorobenzene were analyzed by electron-capture gas-liquid chromatography and nuclear magnetic resonance. The results indicate that the samples are 94.9% 1,2,3,4 and 98.7% 1,2,4,5-tetrachlorobenzene. Gas-liquid chromatography, using an electron-capture detector, was found to be a very sensitive method for detection of tetrachlorobenzene. Amounts as small as 0.01 microg have been detected. The column used was alkaline carbowax 20 M on regular chromosorb (60-80 mesh), with a column temperature of 190 degrees C and an injector temperature of 215 degrees C.