When trichloroacetic acid (TCA) and trichloroethanol (TCE) in the urine of human subjects, rabbits, rats, and guinea-pigs were determined by Seto and Schultze's (1956) method, the recovery of TCE, added to urine, varied widely from 81·3% in guinea-pig urine to 16·2% in rat urine. To obtain the maximum recovery of added TCE, Seto and Schultze's method was further modified to give satisfactory results (recovery rate of 95·9 to 98·5%) when applied to human urine as well as to the urine of the above species of animals. Urine samples from human subjects as well as from rats exposed to trichloroethylene were analysed by this modified method. The results showed that the ratio of TCE to TCA varies as a function of environmental trichloroethylene concentration, indicating that the determination of total trichlorocompounds gives a better index of trichloroethylene exposure than does the determination of TCA alone.