A selected ion monitoring gas chromatography/mass spectrometric method for the quantitative determination of 3,4,4'-trichlorocarbanilide (TCC) and its major metabolites (the 2'-hydroxy sulfate and the N- and N'-glucuronides) in human plasma and urine was developed using the deuterium-labelled compounds as internal standards. Limits of detection of 3 ng/mL in urine for the N-glucuronides and of 1.5 ng/mL in plasma for the 2'-hydroxy sulfate were attained. Use of the method was illustrated in a study in human subjects employing TCC-containing bar soaps.