A gas chromatographic procedure is described which permits quantification of dichloroacetic acid in urine or plasma to a lower limit of about 0.04 μg/ml. Preliminary data are given to suggest that the method should be equally applicable to the determination of trichloroacetic acid. The procedure involves making the sample slightly alkaline to convert the dichloroacetic acid to its sodium salt, lyophilization, esterification with boron trifluoride-methanol, addition of water to destroy unreacted boron trifluoride-methanol complex, and extraction of the ester into benzene. An aliquot of the benzene is then injected onto a Chromosorb 101 chromatographic column, utilizing a tritium foil electron capture detector. The range of linearity appears to be about 0–3 ng of dichloroacetic acid (as the methyl ester) injected on column.