The metabolism of the xenobiotics 1,1,1-trichloroethane (TCE) or 1,1,2-trichloro-1,2,2-trifluoroethane and endogeneous substrates may be changed under physiological stress situations. We studied long-term effects on rats exposed to TCE, noise pollution, and their combination. The experiments were performed in a special set-up where four parallel groups of rats were simultaneously exposed to defined conditions the chemical vapor; the noise pollution of 90 dB; their combination; and a control group without any exposure. The vapor of TCE was applied at a concentration of 200 ppm/8 hr or of 2000 ppm/12 hr for 84 days each. The experiments were performed with TCE from two different commercial sources. One of those TCE preparations caused effects at the high dosage level in terms of enhanced levels of the relation of liver to body weight; liver microsomal protein content; liver microsomal monooxygenase activity; and 3,4-dihydroxyphenylglycol excretion in urine. Eight other physiological and biochemical parameters were not changed.